研究者データベース

田地川 浩人(タチカワ ヒロト)
工学研究院 応用化学部門 機能材料化学分野
助教

基本情報

所属

  • 工学研究院 応用化学部門 機能材料化学分野

職名

  • 助教

学位

  • 工学博士(北海道大学)
  • 工学修士(北海道大学)

論文上での記載著者名

  • Hiroto Tachikawa

ホームページURL

J-Global ID

研究キーワード

  • 分子設計理論   

研究分野

  • ナノテク・材料 / ナノバイオサイエンス
  • ナノテク・材料 / ナノ材料科学
  • 自然科学一般 / 数理物理、物性基礎
  • ものづくり技術(機械・電気電子・化学工学) / 電子デバイス、電子機器
  • 自然科学一般 / 半導体、光物性、原子物理
  • ナノテク・材料 / 基礎物理化学

職歴

  • 1988年 - 北海道大学助手(大学院工学研究科物質化学専攻) 助手
  • 1988年 - Research Associate

学歴

  •         - 1988年   北海道大学   工学研究科   応用化学専攻博士後期課程
  •         - 1988年   北海道大学
  •         - 1987年   北海道大学   工学研究科   応用化学専攻
  •         - 1987年   北海道大学
  •         - 1985年   北海道大学   工学部   応用化学科
  •         - 1985年   北海道大学

所属学協会

  • 日本放射線化学会   日本化学会   アメリカ化学会   

研究活動情報

論文

  • Hiroto Tachikawa
    SURFACE SCIENCE 691 2020年01月 [査読有り][通常論文]
     
    The efficiency of metal storage in carbon materials directly affects battery performance. Therefore, elucidating the storage mechanism is important for developing high-efficiency and new storage materials. In this study, interatomic interactions between Li species (Li atoms and Li+ ions) and graphene nanoflakes (GRs) have been investigated using the density functional theory method to elucidate the mechanism of Li storage on GRs. Moreover, single, double, and triple Li species were examined. For single Li systems (it = 1), the binding energy and diffusion barrier of Li on GRs were investigated, while the interatomic interactions and packing structures of Li species on GRs were investigated for double and triple Li systems (n = 2 and 3, respectively). The diffusion barriers for Li+ and Li for n = 1 were calculated to be 5.90 and 6.84 kcal/mol, respectively. For n = 2, the diffusion was strongly affected by the counter Li species and was attributed to the repulsive interactions. For n = 2, the close packing configurations of Li species on the surface of the GRs consisted of biphenyl structures where Li species were located inside the benzene rings of the biphenyl-like site of GRs. For n = 3, three Li species were bound to the triphenylene sites (two biphenyl-like sites). The electronic states of the Li species stored on GRs were discussed using the theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 58 12 2019年12月 [査読有り][通常論文]
     
    The functionalization of fullerenes, which are excellent n-type materials, has received much attention. The substituents enable tuning of the electronic state and fixing to the substrate. In this study, to elucidate the hydrofluorination mechanism of C-60 fullerene, reaction mechanisms involving one or two hydrogen fluoride (HF) molecules were investigated by means of density functional theory. The hydrofluorination of C-60 in the gas phase is an electrophilic addition reaction with only the 1,2-addition being an exothermic. The activation energy of hydrofluorination by two molecules of HF is about 30kcalmol(?1) lower than that with one molecule of HF. This is because hydrogen bonds between HF molecules are involved in the stabilization of the reactant and the aromaticity improvement of the transition state. These results suggest that hydrofluorination can be controlled by the size of the HF cluster.
  • Hiroto Tachikawa, Hiroshi Kawabata
    SOLID STATE SCIENCES 97 2019年11月 [査読有り][通常論文]
     
    The electronic states and band gaps of carbon materials such as graphene, fullerene, and carbon nanotubes are strongly affected by radical addition. In the present study, the reactions of graphene nanoflakes with fluorine (F) atoms were investigated by density functional theory (DFT) in order to elucidate the nature of the bonding between the F atoms and the graphene nanoflakes. Graphene nanoflakes composed of 4-37 benzene rings were used as graphene models. The present calculations reveal that F atoms react with graphene surfaces and bind directly to carbon atoms to form strong C-F bonds. The binding sites are locally C delta+-F delta- polarized and have large dipole moments. The binding energy of F to graphene was calculated to be 30 kcal/mol, which is 1.5 times larger than that for the addition of hydrogen. Fluorine atoms also add to these surfaces without activation barriers, which is very different to hydrogen-addition reactions that have barriers of 5-6 kcal/mol. The electronic states of the fluorinated graphenes are discussed on the basis of the theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 58 6 061010 - 061010 2019年06月 [査読有り][通常論文]
     
    Gallium-doped zinc oxide films prepared by atomic layer deposition have received much attention. When triethylgallium is hydrolyzed on the surface of zinc hydroxide, a multi-layered metal oxide film containing a specific amount of gallium at a controlled position is formed. In this study, to elucidate the micro-hydrolysis mechanism of triethylgallium, reaction mechanisms involving one or two water molecules were investigated by molecular orbital calculations. The complete hydrolysis of triethylgallium occurs in three steps with the first partial hydrolysis being the rate limiting step. The activation energy of hydrolysis by two molecules of water is similar to 10 kcal mol(-1) lower than that with one molecule of water for all steps. The addition of further water molecules significantly decreases the activation energy because the transition state is stabilized by hydrogen bonding between the water molecules. These results suggest the hydrolysis reaction proceeds spontaneously under mild conditions by controlling the concentration of water molecules. (C) 2019 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 123 22 4743 - 4749 2019年06月 [査読有り][通常論文]
     
    Carbon dioxide (CO2) is one of the stable and inactive molecules that contribute to greenhouse gases. The development of new reactions of CO, activation, chemical fixation, and conversion is a very important issue. In this report, the reactions of CO2-H2O binary clusters were investigated using a direct ab initio molecular dynamics (AIMD) method to find a new reaction of CO, activation. Clusters composed of carbon dioxide and water molecules, CO2 (H2O)(n) (n = 2-5), were utilized as a model of the binary cluster. The reaction dynamics of [CO2 (H2O)(n)](+) following the ionization of parent neutral clusters were also investigated. Two electronic states of [CO2(H2O)(n)](+) were examined for direct AIMD surfaces: [CO2(H2O)(n)](+) (ground state) and (CO2 ) + (H2O)(n) (excited charge transfer (CT) state). After the ionization of the clusters, a proton-transfer (PT) reaction occurred within the (H2O)(n)(+) moiety at the ground state, whereas the reactive HCO3 radical was formed at the CT state for OH addition to CO2+ : + CO2+(H2O)(n) -> HCO3 +H- (+)(H2O)(n-)(1). The mechanisms of the PT process and the HCO3 radical formation were discussed based on the theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama
    JOURNAL OF PHYSICAL CHEMISTRY C 123 14 8709 - 8716 2019年04月 [査読有り][通常論文]
     
    Carbon materials, such as graphene nanoflakes, carbon nanotubes, and fullerenes, can be used for hydrogen storage. Alkali doping of these materials generally increases their H-2-storage density. In this study, the interaction of hydrogen molecules with Li-doped graphene nanoflakes was systematically investigated using density functional theory (DFT). A large polycyclic aromatic hydrocarbon composed of 37 benzene rings (referred to as GR) was used as a model of a graphene nanoflake, and GR-Li-(H-2) and GR-Li+-(H-2)(n), (n = 0-13) clusters were used as hydrogen storage systems. The first and second coordination shells of H2 around GR-Li were saturated at n = 3 and 7, respectively. The binding energy of H-2 to GR-Li decreased with increasing n, reaching a limiting value at n = 10. For GR-Li+-(H-2)(n), similar results were obtained and the Li atom on GR was shown to be activated by electron transfer from Li to GR. The diffusion barrier of Li+ on GR decreased upon addition of H-2 to Li+ from 6.35 (n = 0) to 3.62 kcal/mol (n = 4). The mechanism of H-2 addition is discussed herein based on the calculated results.
  • Hiroto Tachikawa, Ryoshu Iura, Hiroshi Kawabata
    SCIENTIFIC REPORTS 9 2377 - 2377 2019年02月 [査読有り][通常論文]
     
    Single molecule electron devices (SMEDs) have been widely studied through both experiments and theoretical calculations because they exhibit certain specific properties that general macromolecules do not possess. In actual SMED systems, a residual water molecule strongly affects the electronic properties of the SMED, even if only one water molecule is present. However, information about the effect of H2O molecules on the electronic properties of SMEDs is quite limited. In the present study, the effect of H2O on the ON-OFF switching property of benzene-based molecular devices was investigated by means of a direct ab initio molecular dynamics (AIMD) method. T- and H-shaped benzene dimers and trimers were examined as molecular devices. The present calculations showed that a H2O molecule accelerates the pi-stacking formation in benzene molecular electronic systems. The times of stacking formation in a benzene dimer cation (n = 2) were calculated to be 460 fs (H2O) and 947 fs (no-H2O), while those in a trimer cation (n = 3) were 551 fs (H2O) and 1019 fs (no-H2O) as an average of the reaction time. This tendency was not dependent on the levels of theory used. Thus, H2O produced positive effects in benzene-based molecular electronics. The mechanism of pi-stacking was discussed based on the theoretical results.
  • Hiroto Tachikawa
    SURFACE SCIENCE 679 196 - 201 2019年01月 [査読有り][通常論文]
     
    The interaction and reaction of methyl radical (CH3) with polycyclic aromatic hydrocarbons (PAHs) have been investigated by means of density functional theory (DFT) to systematically elucidate the binding nature of CH3 to graphene nanoflakes. PAHs with n = 4-37, where n indicates the number of benzene rings, were chosen as graphene nanoflakes. The activation energies for the addition of CH3 to the graphene surface were found to be almost constant, with values in the range 13.0-15.0 kcal/mol at the CAM-B3LYP/6-311G(d,p) level, for all PAHs. The binding energies between CH3 and the graphene surfaces were slightly dependent on the size (n): 1.0-4.2 kcal/mol. The absorption spectra showed that a long tail is generated in the low-energy region after CH3 addition to the graphene surfaces. The electronic states of the CH3-added graphenes were discussed on the basis of theoretical results
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 122 16 4121 - 4129 2018年04月 [査読有り][通常論文]
     
    The benzene radical cation (Bz(+)) is a typical model molecule of the Jahn-Teller (J-T) active species. Bz(+) has two structural forms due to the J-T effect. These are the compressed and elongated forms, expressed as Bz(+)(comp) and Bz(+)(elong), respectively. In Bz(+)(comp), the hexagonal structure of the benzene ring is compressed up and down, and in Bz+(elong), it is pulled up and down. From electron spin resonance experiments, it was found that Bz(+) takes a compressed form in low temperature Freon matrices (CF3CI and CF2ClCFCl2), whereas the elongated form was found in argon matrices. However, the selectivity of these structural forms is still unclear. In this study, the ionization dynamics of isolated benzene (Bz) and benzene-M complexes (where M denotes counter-molecules, M = NH3, H2O, CF3Cl, CH4, CH3OH, Ar, SH2, ammonia dimer, or water dimer) have been investigated by means of the direct ab initio molecular dynamics (AIMD) method in order to shed light on the Bz(+) formation mechanism. The static ab initio calculations showed that Bz(+)(comp) is slightly more energetically stable than Bz(+)(elong), although the energy difference was only 0.1 kcal/mol at the CCSD/6-311++G(d,p) level. The direct AIMD calculations indicated that Bz(+)(comp) was formed from the Bz-M complexes when M was NH3, CF3Cl, or an ammonia dimer, whereas the ionization of Bz-M when M was H2O, CH4, CH3OH, SH2, or a water dimer formed Bz(+)(elong). In the case of complexes with an argon dimer, Bz(Ar)(2), both forms were obtained from a slight orientation change of Ar on Bz. A selective rule is discussed on the basis of the calculated results.
  • Hiroto Tachikawa, Yoshiyuki Miyazawa, Ryoshu Iura
    CHEMISTRYSELECT 3 4 1113 - 1119 2018年01月 [査読有り][通常論文]
     
    The pi-stacking interaction plays a crucial role in structural arrangements and molecular assemblies in several molecular systems. In the present study, pi-stacking formation in the benzene trimer cation, (Bz)(3)(+), following ionization of the parent neutral benzene trimer, (Bz)(3), was investigated using direct ab initio molecular dynamics to elucidate the timescale of pi-stacking formation and reaction mechanism in the ionized state. Cyclic (Bz)(3) was chosen as the benzene cluster. After ionizing (Bz)(3), the structure drastically changed to a double pi-stacking form. The (Bz)(3)(+) product vibrated between two structural forms, (Bz-Bz(c))(+)Bz Bz(Bz(c)-Bz)(+), where Bz(c) is a benzene molecule located in the central position of (Bz)(3)(+) and (Bz(c)-Bz)(+) represents a dimer core composed of the benzene dimer cation. The timescale of pi-stacking formation was calculated as 300-380 fs. The absorption spectrum of (Bz)(3)(+) was blue-shifted as a function of time. We discuss the reaction mechanism based on the theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY 17 12 8835 - 8841 2017年12月 [査読有り][通常論文]
     
    Functionalized fullerene, graphene, and carbon nanotubes are known as high-performance molecular devices. In this work, the electronic structures and formation mechanism of hydrogen-functionalized fullerene were investigated by means of density functional theory. The mechanism of the addition of a hydrogen atom to the fullerene surface was mainly investigated. Both pure and boron-nitrogen-substituted fullerenes (denoted by C-60 and BNC58, respectively) were examined. We found that the addition of hydrogen atom to B (boron atom) and C (carbon atom) sites of BNC58 proceeded without an activation barrier, whereas the hydrogenation of N (nitrogen atom) sites required activation energy. The electronic states of hydrogen-functionalized C-60 and BNC58 are discussed on the basis of these theoretical results.
  • Hiroto Tachikawa, Kazuko Haga, Kazuo Yamada
    COMPUTATIONAL AND THEORETICAL CHEMISTRY 1115 175 - 178 2017年09月 [査読有り][通常論文]
     
    Since the accident at the Fukushima nuclear power plant, the removal of radioactive cesium ions (Cs-137(+)) from wastewater has become an important topic. Nickel ferrocyanide (Ni-FeCN) is known to adsorb Cs-137(+) preferentially from radioactive waste solutions. However, the mechanism underlying the selectivity of Ni-FeCN is not clearly understood. In the present study, the ion selectivity of Ni-FeCN was investigated by means of density functional theory (DFT) calculations to determine why Ni-FeCN selectively adsorbs Cs+. Models of the interactions of Cs+ and K+ with Ni-FeCN were examined via DFT calculations, which revealed that the hydration energy of Cs+ plays an important role in its selective adsorption by Ni-FeCN. The electronic states of Cs+/K+ in Ni-FeCN are discussed based on the theoretical results. (C) 2017 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 121 28 5237 - 5244 2017年07月 [査読有り][通常論文]
     
    Reactions of the microhydrated hydrogen chloride radical cation, [HCl-(H2O)(n)](+) (n = 1-5), following the ionization of,the parent neutral cluster were investigated by the direct ab initio molecular dynamics (AIMD) method to elucidate the cluster size dependence of the proton transfer (PT) rate in the ionized state. The ionization occurred from the HCl moiety of the clusters. The proton of HCl+ was transferred to the neighboring water molecule in the cluster. The time of PT was strongly dependent on the cluster size (n); the time of PT decreased with increasing n and reached a limiting value at n = 4-5 (the time of PT was ca. 7 fs). The acceleration of the PT rate was mainly caused by the shortness of the hydrogen bond between HCl+ and H2O in larger clusters, that is, a short hydrogen bond causes fast PT. The electrostatic effects of the water cluster further accelerated the rate of PT. After the first PT from HCl+ to H2O, the second PT (H3O+ + H2O -> H2O + H3O+) was detected for n = 3-5. The times of the first and second PTs were calculated as 7-15 and 30-40 fs, respectively.. The reaction mechanism was discussed based on the theoretical results.
  • Hiroshi Kawabata, Hiroto Tachikawa
    C-JOURNAL OF CARBON RESEARCH 3 2 2017年06月 [査読有り][通常論文]
     
    The smallest fullerene C-20 with positive electron affinity is considered to be a new organic nano-electronic material. The binding structures and electronic states of lithium ions and atoms (Li+ and Li) trapped on the surface of C-20 have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of their interaction. It was found that a Li+ can bind to only one site of C-20. This is, specifically, on top of the site where Li+ binds to the carbon atom of C-20. On the other hand, in the case of a Li atom, two structures were obtained besides the on-top structure. One was pentagonal structure which included a Li atom on a five-membered ring of C-20. The other was a triangular structure in which the Li atom bind to the the carbon-carbon bond of C-20. Finally, the nature of the interactions between Li ions or atoms and the C-20 cluster was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF COMPUTATIONAL CHEMISTRY 38 17 1503 - 1508 2017年06月 [査読有り][通常論文]
     
    Reactions of water dimer cation (H2O)(2)(1) following ionization have been investigated by means of a direct ab initio molecular dynamics method. In particular, the effects of zero point vibration and zero point energy (ZPE) on the reaction mechanism were considered in this work. Trajectories were run on two electronic potential energy surfaces (PESs) of (H2O)(2)(+) : ground state ((2) A ''-like state) and the first excited state ((2)A '-like state). All trajectories on the ground- state PES lead to the proton- transferred product: H2O+(Wd)center dot H2O(Wa) -> OH(Wd)center dot H3O+(Wa), where Wd and Wa refer to the proton donor and acceptor water molecules, respectively. Time of proton transfer (PT) varied widely from 15 to 40 fs (average time of PT=30.9 fs). The trajectories on the excited- state PES gave two products: an intermediate complex with a face- to- face structure (H2O-OH2)(+) and a PT product. However, the proton was transferred to the opposite direction, and the reverse PT was found on the excited- state PES: H2O(Wd)center dot H2O+ (Wa) -> H3O+ (Wd)center dot OH( Wa). This difference occurred because the ionizing water molecule in the dimer switched between the ground and excited states. The reaction mechanism of (H2O)(2)(+) and the effects of ZPE are discussed on the basis of the results. (C) 2017 Wiley Periodicals, Inc.
  • Hiroto Tachikawa
    CHEMICAL PHYSICS 490 12 - 18 2017年06月 [査読有り][通常論文]
     
    Biphenyl (Bp) and its related compounds are widely applied in single-molecule electronic devices. In this study, the effects of micro-solvation on the hole capture (ionization) dynamics of Bp were investigated by means of direct ab initio molecular dynamics (AIMD) simulations. The micro-solvation of Bp was simulated using one and two water molecules (i.e., Bp(H2O)(n) (n = 0-2)). The reaction dynamics of Bp(+)(H2O)(n)). following hole capture were investigated via direct AIMD simulation. In the case without H2O (n = 0), the twist angle of Bp(+) periodically vibrated without decay. In contrast, when water molecules were near Bp(+), the amplitude of the twist angle vibration decayed periodically. The formation of hydrogen bonds between Bp(+) and water molecules prevents periodic vibration by generating friction. The electronic states and reaction mechanism were investigated based on the theoretical results. (C) 2017 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    APPLIED SURFACE SCIENCE 396 1335 - 1342 2017年02月 [査読有り][通常論文]
     
    Polycyclic aromatic hydrocarbons (PAHs) provide a 2-dimensional (2D) reaction surface in 3-dimensional (3D) interstellar space and have been utilized as a model of graphene surfaces. In the present study, the reaction of PAHs with atomic hydrogen was investigated by means of density functional theory (DFT) to systematically elucidate the binding nature of atomic hydrogen to graphene nanoflakes. PAHs with n = 4-37 were chosen, where n indicates the number of benzene rings. Activation energies of hydrogen addition to the graphene surface were calculated to be 5.2-7.0 kcal/mol at the CAM-B3LY13/6-311G(d,p) level, which is almost constant for all PAHs. The binding energies of hydrogen atom were slightly dependent on the size (n): 14.8-28.5 kcal/mol. The absorption spectra showed that a long tail is generated at the low-energy region after hydrogen addition to the graphene surface. The electronic states of hydrogenated graphenes were discussed on the basis of theoretical results. (C) 2016 Published by Elsevier B.V.
  • Saori Yoshizawa, Shigeaki Abe, Mami Mutoh, Teruo Kusaka, Mariko Nakamura, Yasuhiro Yoshida, Junichiro Iida, Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 56 1 2017年01月 [査読有り][通常論文]
     
    Oligosilane-functionalized C-60 fullerenes [namely, C-60-(SiH2)(n)-H, n = 1-4] have been investigated by the density functional theory (DFT) method to elucidate the structures and electronic states of oligosilane-radical added fullerene. The DFTcalculation showed that oligosilane radicals bind to the carbon atom of C60 in the on-top site, and a strong Si-C heterojunction is formed. The binding energies of oligosilane radicals to C-60 were calculated to be 24.6-28.2 kcal/mol at the CAM-B3LYP/6-311G(d, p) level. The electronic states of oligosilane-functionalized fullerenes C-60-(SiH2)(n)-H are discussed on the basis of theoretical results. (C) 2017 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 120 37 7301 - 7310 2016年09月 [査読有り][通常論文]
     
    The ice surface provides an effective two-dimensional reaction field in interstellar space. However, how the ice surface affects the reaction mechanism is still unknown. In the present study, the reaction of an ammonia dimer cation adsorbed both on water ice and cluster surface was theoretically investigated using direct ab initio molecular dynamics (AIMD) combined with our own n-layered integrated molecular orbital and molecular mechanics (ONIOM) method, and the results were compared with reactions in the gas phase and on water clusters. A rapid proton transfer(PT) from NH3+ to NH3 takes place after the ionization and the formation of intermediate complex NH2(NH4+) is found. The reaction rate of PT was significantly, affected by the media connecting to the ammonia dimer. The time of PT was calculated to be SO fs (in the gas phase), 38 fs (on ice), and 28-33 fs (on water clusters). The dissociation of NH2(NH4+) occurred on an ice surface. The reason behind the reaction acceleration on an ice surface is discussed.
  • Hiroto Tachikawa, Tomoya Takada
    COMPUTATIONAL AND THEORETICAL CHEMISTRY 1089 13 - 20 2016年08月 [査読有り][通常論文]
     
    The proton transfer (PT) reaction after water cluster ionization is known to be a very fast process occurring on the 10-30 fs time scale. In the present study, the ionization dynamics of the branched water tetramer (H2O)(4) were investigated by means of a direct ab initio molecular dynamics (AIMD) method to elucidate the time scale of PT in the water cluster cation. A long-lived non-proton-transferred intermediate was found to exist after the ionization of the branched-type water cluster. The lifetimes of the intermediate were calculated to be ca. 100-150 fs. PT occurred after the formation of the intermediate. The structure of the intermediate was composed of a symmetric cation core: H2O-H2O+-H2O. The broken symmetry of the structure led to PT from the intermediate. The reaction mechanism is discussed based on the theoretical results. (C) 2016 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY A 120 33 6596 - 6603 2016年08月 [査読有り][通常論文]
     
    The mechanism by which CO2 is formed in the interstellar space remains a mystery. The most likely reaction is collision between CO and OH; however, previous theoretical works have shown that the activation barrier for CO2 formation is high enough to prevent the reaction at the low thermal conditions of space (similar to 10 K). The effects of single water molecule on the reaction barrier of CO, formation from reaction between CO and OH have been investigated here by means of ab initio calculation. The barrier height along the lowest-energy pathway in the reaction between CO and OH in the absence of the H2O molecule was calculated to be 2.3 kcal/mol when CCSD(T) energy corrections are combined with the MP2 basis set limit. In the case of the hydrated (H2O-CO-OH) system, the inclusion of a single H2O molecule into the system significantly decreased the barrier height to 0.2 kcal/mol. This suggests that CO2 can be formed when CO and OH react in the presence of H2O, even under thermal conditions as low as 10 K.
  • Hiroto Tachikawa, Tomoya Takada
    CHEMICAL PHYSICS 475 9 - 13 2016年08月 [査読有り][通常論文]
     
    The surfaces of icy planets and comets are composed of frozen water (H2O), carbon dioxide (CO2), and methane (CH4). These surfaces are irradiated by solar wind and cosmic rays from the interstellar space and they cause ionization of surface molecules. In this report, the effects of ionization of cold water clusters have been investigated using a direct ab initio molecular dynamics (AIMD) method to elucidate the rate of proton transfer (PT) in cations of small water clusters (H2O)(n) (n = 2-7). After ionization of the water clusters, PT occurred in all the cluster cations, and dissociation of the OH radical occurred for n = 4-7. The time of PT decreased with increasing the cluster size at n = 2-5 and reached a limiting value at n = 6 and 7. The mechanism of the PT process in ionized water clusters was discussed based on the theoretical results. (C) 2016 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 6 2016年06月 [査読有り][通常論文]
     
    Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz)(n) (n = 1-4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR-(Bz)(n) (n = 1-4) showed that the aryl radical binds to the carbon atom of GR, and a C-C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol(-1) at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol(-1). The electronic states of GR-( Bz) n were examined on the basis of theoretical results. (C) 2016 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    SURFACE SCIENCE 647 1 - 7 2016年05月 [査読有り][通常論文]
     
    The solid surface provides an effective two-dimensional reaction field because the surface increases the encounter probability of bi-molecular collision reactions. Also, the solid surface stabilizes a reaction intermediate because the excess energy generated by the reaction dissipates into the bath modes of surface. The ice surface in the universe is one of the two dimensional reaction fields. However, it is still unknown how the ice surface affects to the reaction mechanism. In the present study, to elucidate the specific property of the ice surface reaction, ionization dynamics of water dimer adsorbed on the ice surface was theoretically investigated by means of direct ab-initio molecular dynamics (AIMD) method combined with ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) technique, and the result was compared with that of gas phase reaction. It was found that a proton is transferred from H2O+ to H2O within the dimer and the intermediate complex H3O+ (OH) is formed in both cases. However, the dynamic features were different from each other. The reaction rate of the proton transfer on the ice surface was three times faster than that in the gas phase. The intermediate complex H3O+(OH) was easily dissociated to H3O+ and OH radical on the ice surface, and the lifetime of the complex was significantly shorter than that of gas phase (100 fs vs. infinite). The reason why the ice surface accelerates the reaction was discussed in the present study. (C) 2015 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    SOLID STATE SCIENCES 55 138 - 143 2016年05月 [査読有り][通常論文]
     
    Electronic structures and formation mechanism of hydrogen functionalized carbon nanotube (CNT) have been investigated by means of density functional theory (DFT) method. The mechanism of hydrogen addition reaction to the CNT surface was also investigated. Pure and boron-nitrogen (BN) substituted CNT (denoted by CNT and BN-CNT, respectively) were examined as the carbon nanotubes. It was found that the additions of hydrogen atom to B (boron atom) and C (carbon atom) sites of BN-CNT proceed without activation barrier, whereas the hydrogenation of N (nitrogen atom) site needs the activation energy. The electronic states of hydrogen functionalized CNT and BN-CNT were discussed on the basis of theoretical results. (C) 2016 Elsevier Masson SAS. All rights reserved.
  • Mami Mutoh, Shigeaki Abe, Teruo Kusaka, Mariko Nakamura, Yasuhiro Yoshida, Junichiro Iida, Hiroto Tachikawa
    ATOMS 4 1 2016年03月 [査読有り][通常論文]
     
    The ternary interaction system composed of fluorinated ethylene carbonate, denoted by EC(F), lithium ion (Li+) and a model of nano-structured graphene has been investigated by means of the density functional theory (DFT) method. For comparison, fluorinated vinylene carbonate, denoted by VC(F), was also used. The model of graphene consisting of 14 benzene rings was examined as a nano-structured graphene. The effects of fluorine substitution on the electronic state and binding energy were investigated from a theoretical point of view. It was found that both EC(F) and VC(F) bind to a hexagonal site corresponding to the central benzene ring of the model of the graphene surface. The binding energies of Li+EC(F) and Li+VC(F) to the model of graphene decreased with increasing number of fluorine atoms (n).
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY A 120 9 1529 - 1535 2016年03月 [査読有り][通常論文]
     
    To design theoretically the high-performance proton switching element based on DNA base pair, the effects of fluorine substitution on the rate of proton transfer (PT) in the DNA model base pair have been investigated by means of direct ab initio molecular dynamics (AIMD) method. The 2-amino-pyridine dimer, (AP)(2), was used as the model of the DNA base pair. One of the hydrogen atoms of the AP molecule in the dimer was substituted by a fluorine (F) atom, and the structures, of the dimer, expressed by F-(AP)(2), were fully optimized at the MP2/6-311++G(d,p) level. The direct AIMD calculations showed that the proton is transferred within the base pair after the vertical ionization. The rates of PT in F-(AP)(2)(+) were calculated and compared with that of (AP)(2)(+) without an F atom. It was found that PT rate is accelerated by the F-substitution. Also, the direction of PT between F-AP and AP molecules can be clearly controlled by the position of F-substitution (AP)(2) in the dimer.
  • Shigeaki Abe, Shimpei Kawano, Yu Toida, Mariko Nakamura, Satoshi Inoue, Hidehiko Sano, Yasuhiro Yoshida, Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 3 2016年03月 [査読有り][通常論文]
     
    The structures and electronic states of alkyl-radical-functionalized C-20 fullerenes (denoted by C-20-R) have been investigated using density functional theory (DFT). The different alkyl radicals investigated were methyl, ethyl, propyl, and butyl radicals. The DFT calculation indicated that the alkyl radical binds to the carbon atom of C-20 in the on-top site, thus forming a strong C-C single bond. The binding energies of the alkyl radicals to C-20 were calculated to be 83.9-86.6 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The electronic states of the C-20-R complex are discussed on the basis of the theoretical results. (C) 2016 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 55 2 2016年02月 [査読有り][通常論文]
     
    Functionalized fullerenes are known as a high-performance molecules. In this study, the alkyl-functionalized fullerenes (denoted by R-C-60) have been investigated by means of the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of fullerene. Also, the reaction mechanism of alkyl radicals with C-60 was investigated. The methyl, ethyl, propyl, and butyl radicals (denoted by n = 1-4, where n means the number of carbon atoms in the alkyl radical) were examined as alkyl radicals. The DFT calculation showed that the alkyl radical binds to the carbon atom of C-60 at the on-top site, and a strong C-C single bond is formed. The binding energies of alkyl radicals to C-60 were distributed in the range of 31.8-35.1 kcal mol(-1) at the CAM-B3LYP/6-311G(d, p) level. It was found that the activation barrier exists before alkyl addition, the barrier heights were calculated to be 2.1-2.8 kcal mol(-1). The electronic states of R-C-60 complexes were discussed on the basis of the theoretical results. (C) 2016 The Japan Society of Applied Physics
  • Hiroto Tachikawa
    THEORETICAL CHEMISTRY ACCOUNTS 135 3 1 - 9 2016年02月 [査読有り][通常論文]
     
    Ionizing radiation to DNA induces sometimes the DNA damage. In this report, the ionization dynamics of uracil dimer (U)(2) and its water complex (U)(2)-H2O have been investigated by means of direct ab initio molecular dynamics (AIMD) method in order to elucidate the effects of single water molecule on the reaction rate of proton transfer (PT) in DNA model base pair. The (U)(2) dimer is widely used as a simplified mimetic model of Watson-Crick base pair. The static ab initio calculation showed that two conformers exist as neutral complex of (U)(2)-H2O. The direct AIMD calculation of ionization process of (U)(2)-H2O showed that the rate of PT is affected even by a single water molecule, while it was dependent on the position of H2O around (U)(2). The interaction of water molecule with (U)(2) affected the potential energy curve for PT. Especially, the activation barrier along the PT coordinate was significantly changed by the interaction with one H2O molecule. The effects of one H2O molecule on the PT process were discussed on the basis of theoretical results.
  • Tachikawa Hiroto, Kawabata Hiroshi
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 116 2 123 - 129 2016年01月15日 [査読有り][通常論文]
  • Hiroto Tachikawa, Hiroshi Kawabata
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 116 2 123 - 129 2016年01月 [査読有り][通常論文]
     
    High energy irradiation to the hydrogen bonded system is important in relevance with the initial process of DNA and enzyme damages. In the present study, the effects of radiation to catalytic triad have been investigated by means of direct ab-initio molecular dynamics (AIMD) calculation. As a model of the catalytic triad, Ser-His-Glu residue, which is one of the important enzymes in the acylation reaction, was examined. The ionization and electron attachment processes in Ser-HisGlu were investigated as the radiation effects. The direct AIMD calculation showed that a proton of His is spontaneously transferred to carbonyl oxygen of Glu after the ionization. However, the whole structure of catalytic triad was essentially kept after the ionization. On the other hand, in the case of the electron capture in the model catalytic triad Ser-His-Glu, the dissociation of Glu residue from [Ser-His](2) was found as a product channel. The mechanism of ionization and electron capture process in the catalytic triad was discussed on the basis of theoretical results. (C) 2015 Wiley Periodicals, Inc.
  • Hiroto Tachikawa, Tetsuji Iyama
    SOLID STATE SCIENCES 50 91 - 96 2015年12月 [査読有り][通常論文]
     
    Halogen-functionalized graphenes are utilized as electronic devices and energy materials. In the present paper, the effects of halogen-termination of graphene edge on the structures and electronic states of graphene flakes have been investigated by means of density functional theory (DFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the halogen termination, while the excitation energy is red-shifted. The drastic change showed a possibility as electronic devices such as field-effect transistors. The change of electronic states caused by the halogen termination of graphene edge was discussed on the basis of the theoretical results. (C) 2015 Elsevier Masson SAS. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    SOLID STATE SCIENCES 48 141 - 146 2015年10月 [査読有り][通常論文]
     
    Structures and electronic states of organic inorganic compound of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) with alkali metals, M-n(NTCDA) (M=Li and Na, n = 0-2), have been investigated by means of hybrid density functional theory (DFT) calculations. From the DFT calculations, it was found that the electronic state of the complex at the ground state is characterized by a charge-transfer state expressed by (M)(+)(NTCDA)(-). The alkali metals were bound equivalently to the carbonyl oxygen and ether oxygen atoms of NTCDA. The C=O double bond character of NTCDA was changed to a C-O single bond like character by the strong interaction of M to the C=O and O sites. This change was the origin of the red-shift of the IR spectrum. The UV-vis absorption spectra of M-n(NTCDA) were theoretically predicted on the basis of theoretical results. (C) 2015 Elsevier Masson SAS. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 142 6 064301-064301-8  2015年02月 [査読有り][通常論文]
     
    Metal catalyzed carbon-carbon (C-C) bond formation is one of the important reactions in pharmacy and in organic chemistry. In the present study, the electron and hole capture dynamics of a lithium-benzene sandwich complex, expressed by Li(Bz)(2), have been investigated by means of direct ab-initio molecular dynamics method. Following the electron capture of Li(Bz)(2), the structure of [ Li(Bz)(2)](-) was drastically changed: Bz-Bz parallel form was rapidly fluctuated as a function of time, and a new C-C single bond was formed in the C-1-C-1' position of Bz-Bz interaction system. In the hole capture, the intermolecular vibration between Bz-Bz rings was only enhanced. The mechanism of C-C bond formation in the electron capture was discussed on the basis of theoretical results. (C) 2015 AIP Publishing LLC.
  • Hiroto Tachikawa, Tomoya Takada
    RSC ADVANCES 5 9 6945 - 6953 2015年 [査読有り][通常論文]
     
    A proton transfer process is usually dominant in several biological phenomena such as the energy relaxation of photo-excited DNA base pairs and a charge relay process in Ser-His-Glu. In the present study, the rates of proton transfer along a hydrogen bond in a water cluster cation have been investigated by means of a direct ab initio molecular dynamics (AIMD) method. Three basic clusters, water dimer, trimer and tetramer, (H2O)(n) (n = 2-4), were examined as the hydrogen bonded system. It was found that the rate of the first proton transfer is strongly dependent on the cluster sizes: average time scales of proton transfer for n = 2, 3, and 4 were 28, 15, and 10 fs, respectively, (MP2/6-311++G(d,p) level) suggesting that proton transfer reactions are very fast processes in the three clusters. The second proton transfer was found in n = 3 and 4 (the average time scales for n = 3 and 4 were 120 fs and 40 fs, respectively, after the ionization). The reaction mechanism was discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama
    PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 12, NO 6 12 6 659 - 663 2015年 [査読有り][通常論文]
     
    The addition reaction of methyl radical (CH3) to fullerene (C-60) surface has been investigated by means of density functional theory (DFT) method. The DFT calculation showed that the CH3 radical binds directly to the carbon atom of C-60 and a strong C-C single bond is formed. The binding energy of CH3 to C-60 was calculated to be 35.1 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The potential energy curve plotted as a function of a distance of CH3 from the C-60 surface showed that the CH3 radical can approach to the carbon atom with very low activation barrier: the barrier height was calculated to be 2.8 kcal/mol. The electronic states of CH3-C-60 complex were discussed on the basis of theoretical results.
  • Yoshinori Aoyama, Toshihiro Yamanari, Takurou N. Murakami, Tatsuya Nagamori, Kazuhiro Marumoto, Hiroto Tachikawa, Junji Mizukado, Hiroyuki Suda, Yuji Yoshida
    POLYMER JOURNAL 47 1 26 - 30 2015年01月 [査読有り][通常論文]
     
    We investigated the initial photooxidation mechanism leading to reactive radical formation of polythiophene derivatives by focusing on the differences in the photochemical behaviors of photounstable poly(3-hexylthiophene) (P3HT) and photostable poly (3-octyloxythiophene) (P3OOT). Electron spin resonance measurements revealed that the [P3HT](+center dot) (formed by oxygen doping) decayed, whereas no change was observed in the photostable [P3OOT](+center dot) after light irradiation. Furthermore, the absorption decrease of the [P3HT](+center dot) (P3HT) was suppressed by superoxide dismutase. Therefore, the oxygen dopant is superoxide, which might also initiate the oxidation of P3HT. The photochemical difference between P3HT and P3OOT can be explained by the reaction of an a-proton with superoxide in the case of P3HT.
  • Tetsuya Hama, Hirokazu Ueta, Akira Kouchi, Naoki Watanabe, Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS 5 21 3843 - 3848 2014年11月 [査読有り][通常論文]
     
    Despite the rapid accumulation of structural information about organic materials, the correlation between the surface structure of these materials and their chemical properties, a potentially important aspect of their chemistry, is not fully understood. Here, we show that the amorphous or crystalline structure of a solid benzene surface controls its chemical reactivity toward hydrogen. In situ infrared spectroscopy revealed that cold hydrogen atoms can add to an amorphous benzene surface at 20 K to form cyclohexane by tunneling. However, hydrogenation is greatly reduced on crystalline benzene. We suggest that the origin of the high selectivity of this reaction is the large difference in geometric constraints between the amorphous and the crystalline surfaces. The present findings can lead us to a more complete understanding of heterogeneous reaction systems, especially those involving tunneling, as well as to the possibility of nonenergetic surface chemical modification without undesired side reactions or physical processes.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    JOURNAL OF SOLUTION CHEMISTRY 43 9-10 1676 - 1686 2014年10月 [査読有り][通常論文]
     
    Structures and electronic excitation energies of the benzophenone-water (Bp-H2O) and benzophenone-methanol (Bp-CH3OH) complexes have been investigated by means of density functional theory calculations. The CAM-B3LYP/6-311++G(d,p) and higher level calculations were carried out for the system. The calculations indicate that free Bp has a nonplanar structure with twist angle of 54.2A degrees for two phenyl rings (referred to as I center dot). In the case of the Bp-H2O system, the twist angle of the phenyl rings and structure of the Bp skeleton were hardly changed by hydration (I center dot = 55.1A degrees for Bp-H2O). However, the excitation energies of Bp were drastically changed by this solvation. The time-dependent density functional calculations show that the n-IEuro* transition (S-1 state) is blue-shifted by the solvation, whereas two pi-pi* transitions (S-2 and S-3) were red-shifted. The origin of the specific spectral shifts is discussed on the basis of the theoretical results.
  • Hiroto Tachikawa, Takahiro Fukuzumi
    JOURNAL OF SOLUTION CHEMISTRY 43 9-10 1519 - 1528 2014年10月 [査読有り][通常論文]
     
    Electron detachment dynamics of the hydrated superoxide anion (n = 2) have been investigated by means of the direct ab initio molecular dynamics method. Two electronic states (triplet and singlet states) were examined for the neutral oxygen molecule after the electron detachment. In both electronic states, the dissociation products O-2 + water cluster, were obtained. However, the internal states are essentially different from each other. On the triplet state surface, the O-O stretching mode of O-2(I-3 ) pound is excited as a vibrational mode. On the other hand, the internal mode of the product on the singlet state surface is silent. The reaction mechanism is discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    CHEMPHYSCHEM 15 8 1604 - 1610 2014年06月 [査読有り][通常論文]
     
    The mechanism of dissolution of the Li+ ion in an electrolytic solvent is investigated by the direct ab initio molecular dynamics (AIMD) method. Lithium fluoroborate (Li+BF4-) and ethylene carbonate (EC) are examined as the origin of the Li+ ion and the solvent molecule, respectively. This salt is widely utilized as the electrolyte in the lithium ion secondary battery. The binding of EC to the Li+ moiety of the Li+BF4- salt is exo-thermic, and the binding energies at the CAM-B3LYP/6-311++G(d,p) level for n= 1, 2, 3, and 4, where n is the number of EC molecules binding to the Li+ ion, (EC) n(Li+BF4-), are calculated to be 91.5, 89.8, 87.2, and 84.0 kcalmol(-1) (per EC molecule), respectively. The intermolecular distances between Li+ and the F atom of BF4- are elongated: 1.773 angstrom (n= 0), 1.820 angstrom (n= 1), 1.974 angstrom (n= 2), 1.942 angstrom (n= 3), and 4.156 angstrom (n= 4). The atomic bond populations between Li+ and the F atom for n= 0, 1, 2, 3, and 4 are 0.202, 0.186, 0.150, 0.038, and 0.0, respectively. These results indicate that the interaction of Li+ with BF4- becomes weaker as the number of EC molecules is increased. The direct AIMD calculation for n= 4 shows that EC reacts spontaneously with (EC) 3(Li+BF4-) and the Li+ ion is stripped from the salt. The following substitution reaction takes place: EC+(EC)(3)-(Li+BF4-)->(EC)(4)Li+-(BF4-). The reaction mechanism is discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 118 18 3230 - 3236 2014年05月 [査読有り][通常論文]
     
    Ionization dynamics of water microsolvated sulfur dioxide SO2(H2O)(n) (n = 1-3 and 6) have been investigated by means of direct ab initio molecular dynamics (AIMD) method to elucidate the hydration effects of OH addition reaction to SO2 following the ionization. The calculations showed that the neutral 1:1 complex SO2-H2O has a C-s symmetry and the sulfur of SO2 interacts with the oxygen of H2O with an eclipsed form. In the case of ionization of SO2-H2O 1:1 complex (n = 1), the cation complex composed of [H2O-SO2](+) with a face-to-face form was obtained as the product. The OH addition reactions to SO2 were found in larger systems (n = 2, 3, and 6) following the ionization. The reaction was expressed as SO2+(H2O)(n) -> SO2(OH)center dot center dot center dot H+(H2O)(n-1) (n = 2, 3, and 6). The proton generated as (SO2-H2O)(+) -> (HSO3) + H+ was stabilized by the second water molecule as the reaction: H+ + H2O -> H3O+. These processes occurred and were completed within the cluster. The OH addition mechanism in SO2+(H2O)(n) cluster was discussed on the basis of the present results.
  • Hiroto Tachikawa, Tetsuji Iyama
    THIN SOLID FILMS 554 148 - 153 2014年03月 [査読有り][通常論文]
     
    Electronic structures and band gaps of hydrogenated fullerenes have been investigated by means of density functional theory method. The mechanism of hydrogen addition reaction to the fullerene (C-60) surface was also investigated. Addition of one and two hydrogen atoms was examined in the calculations. The binding energies of the second hydrogen atom to C60H were widely distributed in the range 1.5-3.6 eV. It was found that the bonding energy is strongly dependent on the spin density of carbon atom of C60H. The second hydrogen atom preferentially binds to the neighbor site of the first addition site. The electronic states and excitation energies of C-60-H were discussed on the basis of theoretical results. (C) 2013 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    THIN SOLID FILMS 554 199 - 203 2014年03月 [査読有り][通常論文]
     
    The effects of hydrogenation on the band gap of graphene have been investigated by means of density functional theory method. It is generally considered that the band gap increases with increasing coverage of hydrogen atom on the graphene. However, the present study shows that the band gap decreases first with increasing hydrogen coverage and reaches the lowest value at finite coverage (gamma = 0.3). Next, the band gap increases to that of insulator with coverage from 0.3 to 1.0. This specific feature of the band gap is reasonably explained by broken symmetry model and the decrease of pi-conjugation. The electronic states of hydrogenated graphene are discussed. (C) 2013 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama
    SOLID STATE SCIENCES 28 41 - 46 2014年02月 [査読有り][通常論文]
     
    Functionalized graphenes have been utilized as electronic devices and energy materials. In the present paper, the effects of fluorine-termination of graphene edge on the structures and electronic states of graphene have been investigated by means of density functional theory (OFT) method. It was found that the ionization potential (Ip) and electron affinity of graphene (EA) are blue-shifted by the F-substitution. On the other hand, the excitation energy was red-shifted. The drastic change shows a possibility as electronic devices such as field-effect transistors. The drastic change of electronic states caused by the F-substitution of graphene edge was discussed on the basis of the theoretical results. (C) 2013 Elsevier Masson SAS. All rights reserved.
  • Koichi Kato, Tetsuji Iyama, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 53 2 02BD02.1-02BD02.4  2014年02月 [査読有り][通常論文]
     
    The interactions, of magnesium species (Mg, Mg+, and Mg2+) with a graphene surface have been investigated by the density functional theory (OFT) method. The distances of Mg atoms from the graphene surface were calculated to be 1.80 angstrom (Mg2+), 2.16 angstrom (Mg+), and 4.17 angstrom (Mg) at the Coulomb-attenuating method (CAM)-B3LYP/6-31G(d) level. The binding nature of Mg ions (Mg2+ and Mg+) is caused by the charge transfer interaction; and the Mg atom interacts with the surface via van der Weals (vdW) force. The Mg ions can diffuse via the C-C bond center between hexagonal sites. The barrier heights for the diffusion of Mg2+ and Mg+ on the graphene surface were calculated to be 14.6 and 2.8 kcal/mol, respectively. On the other hand, the diffusion of Mg atoms proceeds with a very low barrier. The mechanism of the interaction of Mg with the graphene surface was discussed on the basis of theoretical results. (C) 2014 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Shigeaki Abe
    ELECTROCHIMICA ACTA 120 57 - 64 2014年02月 [査読有り][通常論文]
     
    Solvent dissociation dynamics from solvated lithium ion solvated by ethylene carbonates (EC) have been investigated by means of direct ab-initio molecular dynamics (AIMD) Method. The lithium ion was solvated by four EC molecules as the first solvation shell. It was found that the solvation number of lithium ion is drastically changed from 4 to 1 when the solvated lithium ion accepts an excess electron. The binding energy of Li-EC decreased to a one-tenth. Finally, the contact ion pair composed of Li+ and EC- was formed as the product. The mechanism of solvent dissociation was discussed on the basis of theoretical results. (C) 2013 Elsevier Ltd. All rights reserved.
  • Hiroto Tachikawa
    RSC ADVANCES 4 1 516 - 522 2014年 [査読有り][通常論文]
     
    Electron detachment dynamics of the hydrated superoxide anion O-2(-)(H2O) have been investigated by means of direct ab initio molecular dynamics (AIMD) methods. Two potential energy surfaces were examined as electronic states of oxygen molecule after the electron detachment of the hydrated superoxide anion: O-2((3)Sigma)(H2O) and O-2((1)Delta)(H2O). In both electronic states, the dissociation products, O-2 + H2O, were obtained. However, the internal states of O-2 were essentially different from each other. On the triplet state surface, the O-O stretching mode of O-2((3)Sigma) was excited, whereas that of O-2((1)Delta) was silent. The reaction mechanism was discussed on the basis of theoretical results.
  • Hiroshi Yoshida, Akitoshi Tomizawa, Hiroto Tachikawa, Shin-ichiro Fujita, Masahiko Arai
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 16 35 18955 - 18965 2014年 [査読有り][通常論文]
     
    The catalytic hydrogenation of 2,4-dinitroaniline using a 0.5 wt% Pt/TiO2 catalyst was investigated in a multiphase medium of tetrahydrofuran (THF) pressurized by CO2 at different pressures and at 323 K. When CO2 pressure was increased, the overall rate of hydrogenation simply decreased but the selectivity to the desired product of 4-nitro-1,2-phenylenediamine increased. The noticeable enhancement of the selectivity to 4-nitro-1,2-phenylenediamine can be explained by chemical reactivities of CO2 molecules. In situ high-pressure FTIR and molecular simulations demonstrate that the dissolved CO2 molecules may interact with amino groups of the substrate and weaken the intra-hydrogen bonding between the amino and 2-nitro groups, which results in the change in the relative reactivity of the two nitro groups, yielding the desired product in a higher selectivity. The change in the intra-and inter-molecular interactions between the substrate and CO2 molecules was theoretically examined by DFT calculations.
  • Tetsuji Iyama, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 579 1 10 - 16 2013年09月 [査読有り][通常論文]
     
    The interaction of carbon free radicals (CH and CCH) with a graphene surface has been investigated by means of density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of graphene surface. These radicals are highly reactive and the radical plays an important part of materials chemistry. The DFT calculation showed that the CH and CCH radicals bind to the bond center of C-C carbon atoms as a carbon bridge and a strong C-CH-C bond (or C-C2H-C bond) is formed. The binding energies of CH and CCH radicals to the graphene were calculated to be 48.2 and 46.2 kcal/mol at the B3LYP/6-31G(d) level of theory. The mechanism of CH radical addition was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    THEORETICAL CHEMISTRY ACCOUNTS 132 7 2013年07月 [査読有り][通常論文]
     
    Mechanism of pi-pi double stacking process of benzene trimer cation has been investigated by means of direct ab initio molecular dynamics method. It was found that H-shaped form of neutral benzene trimer is drastically changed to the pi-pi double stacking form composed of benzene trimer cation following the ionization. Absorption spectrum of charge resonance band of (Bz)(3)(+) was gradually blueshifted as a function of time. Time scale of the double stacking process (the formation of trimer cation from the H-shaped form) was calculated to be 0.7-1.5 ps, which is comparable to that of dimer cation formation. After the ionization of benzene trimer, (Bz)(Bz)c(Bz'), the hole is distributed around three benzene molecules with a branching ratio of (Bz)(+0.3) (Bz)c(+0.4) (Bz')(+0.3), and the structure of (Bz)c(+) was rapidly deformed due to the Jahn-Teller effect. Next, the molecular rotation of central benzene (Bz)c(+) occurred gradually. Immediately, both benzene molecules in the wing positions were also rotated synchronicity. Finally, the pi-pi double stacking form composed of benzene trimer cation was formed. The formation mechanism of benzene trimer cation was discussed on the basis of theoretical results.
  • Yoshinori Aoyama, Toshihiro Yamanari, Nagatoshi Koumura, Hiroto Tachikawa, Masaru Nagai, Yuji Yoshida
    POLYMER DEGRADATION AND STABILITY 98 4 899 - 903 2013年04月 [査読有り][通常論文]
     
    The photooxidation of poly(3-hexylthiophene) (P3HT) has previously been investigated and it is known that the sulfur atom of the thiophene ring is oxidized into sulfur oxides by a hydroxyl radical that arises through hydrogen abstraction at the hexyl side chain at the alpha-position. In this study, in order to further investigate the photooxidation mechanism of the polymer, the side chain at alpha-position was varied and three different polythiophene derivatives with phenyl (P3PhT), tert-pentyl (P3DMPT), and alkoxy (P3OOT) groups were synthesized with no alpha-hydrogens. We observed the differences in the photochemical behavior of the polythiophene derivatives by UV-vis-NIR and FT-IR (ATR) spectroscopy during simulated solar light irradiation. It was found that the photooxidation of P3PhT and P3DMPT progressed in the same way as P3HT, whereas the analogous decomposition of P3OOT was not observed. (C) 2013 Elsevier Ltd. All rights reserved.
  • Hiroto Tachikawa, Tomoya Takada
    CHEMICAL PHYSICS 415 76 - 83 2013年03月 [査読有り][通常論文]
     
    Ionization dynamics of the cyclic water trimer (H2O)(3) have been investigated by means of direct ab initio molecular dynamics (AIMD) method. Two reaction channels, complex formation and OH dissociation, were found following the ionization of (H2O)(3). In both channels, first, a proton was rapidly transferred from H2O+ to H2O (time scale is similar to 15 fs after the ionization). In complex channel, an ion-radical contact pair (H3O+-OH) solvated by the third water molecule was formed as a long-lived H3O+(OH)H2O complex. In OH dissociation channel, the second proton transfer further takes place from H3O+(OH) to H2O (time scale is 50-100 fs) and the OH radical is separated from the H3O+. At the same time, the OH dissociation takes place when the excess energy is efficiently transferred into the kinetic energy of OH radical. The OH dissociation channel is significantly minor, and almost all product channels were the complex formation. The reaction mechanism was discussed on the basis of theoretical results. (C) 2012 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 52 1 2013年01月 [査読有り][通常論文]
     
    The interaction of a hydroxyl OH radical with a graphene surface has been investigated by the density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of the graphene surface. The DFT calculation showed that the OH radical binds directly to the carbon atom of the graphene surface and a strong C-O bond is formed. The binding energies were dependent on the cluster size and were distributed in the 4.1-9.5 kcal/mol range at the B3LYP/6-31G(d) level of theory. The potential energy curve plotted as a function of the distance of OH from the surface carbon showed that the OH radical can bind to the carbon atom with a low activation barrier: the barrier heights for n = 7 and 14 were calculated to be 3.9 and 1.9 kcal/mol, respectively. Also, it was found that the structural change from sp(2) to sp(3)-like hybridization occurs by the approach of the OH radical. (C) 2013 The Japan Society of Applied Physics
  • Hirokazu Tamai, Martina Hafner, Achim Walter Hassel, Hiroto Tachikawa, Kazuhisa Azumi
    PLASMA PROCESSING 19 50 46 85 - 91 2013年 [査読有り][通常論文]
     
    Microplasma was formed in a gap hole made in a quartz plate immersed in various kinds of electrolyte solutions at different concentrations. High-voltage AC was applied to the solution by using a pair of contact-or non-contact electrodes at both sides of the gap hole to ignite microplasma generation. Spectra of the light emitted from the microplasma showed elemental emission lines of the species contained in the solution, and their intensities depended on not only their concentration but also plasma conditions such as plasma temperature. A non-equilibrium plasma state was confirmed from estimated temperature of electrons and OH center dot radicals in the order of thousand and 10 thousand Kelvins. Deformation of the gap hole was observed depending on the polarization condition and species, probably due to high-temperature plasma and also dielectric loss in the gap hole.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 720 60 - 65 2012年12月 [査読有り][通常論文]
     
    Hole capture dynamics of phenyl-capped thiophene (DPT) have been investigated by means of density functional theory (DFT) and direct ab-initio molecular dynamics (AIMD) calculations. DPT has been utilized as a part of organic solar cells. The direct AIMD calculations showed that the twist angle of DPT vibrates periodically after hole capture. (C) 2012 Elsevier B.V. All rights reserved.
  • Shigeaki Abe, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 10 2012年10月 [査読有り][通常論文]
     
    The interaction between fluorinated ethylene carbonate denoted by EC(F) and a graphene surface was investigated using of density functional theory (DFT) method. The interaction system examined was a complex composed of graphene (consisting of 14 benzene rings) and one EC(F) molecule. Ten binding sites of EC(F) binding site on the surface and edge regions of the graphene, were identified as stable points. EC(F) bound to a hexagonal position corresponding to the central of benzene ring on the graphene surface and can also bind to the edge of the graphene. The EC(F) binding energies on the surface and edge sides were 0.5 and 2.8 kcal/mol, respectively. The activation barrier for the diffusion of EC(F) on the graphene surface was significantly low (less than 0.3 kcal/mol), indicating that EC(F) can move freely on the graphene surface. (C) 2012 The Japan Society of Applied Physics
  • Takahiro Fukuzumi, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 10 2012年10月 [査読有り][通常論文]
     
    The interaction of hydroperoxyl radical (OOH) with a graphene surface has been investigated by means of density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of graphene surface. The OOH radical is highly reactive and the radical plays an important part of materials chemistry. The DFT calculation showed that the OOH radical binds to the carbon atom of graphene surface and a strong C-O bond is formed. The binding energies were dependent on the cluster size and were distributed in the range 18-25 kcal/mol at the B3LYP/6-31G(d) level of theory. The potential energy curve plotted as a function of C-OOH bond distance showed that the OOH radical approaches to the carbon atom with an activation barrier (the barrier height is distributed in 20-25 kcal/mol). Also, it was found that structural change from sp(2) to sp(3)-like hybridization occurs by the approach of OOH. (C) 2012 The Japan Society of Applied Physics
  • Tomoya Takada, Hiroshi Kawabata, Hiroto Tachikawa
    JOURNAL OF MOLECULAR STRUCTURE 1020 1 - 5 2012年08月 [査読有り][通常論文]
     
    Hydrogen transfer reactions at the ground and excited states of tert-butyl radical to form iso-butyl radical have been investigated by means of ab initio calculation and electron spin resonance (ESR) spectroscopy. It was found that tert-butyl radical irradiated with 254 nm ultraviolet light converts quite efficiently to iso-butyl radical. Also, it was suggested that this conversion occurs as an intramolecular hydrogen transfer from a methyl group of tert-butyl radical to a radical site (central carbon atom). The theoretical calculations showed that barrier height of hydrogen transfer at the excited state is significantly lower than that of ground state. The mechanism of internal hydrogen atom conversion from tert-butyl to iso-butyl radicals was discussed. (C) 2012 Elsevier B.V. All rights reserved.
  • Takeshi Sakamoto, Hiroto Tachikawa, Kazuhisa Azumi
    APPLIED SURFACE SCIENCE 258 18 6785 - 6792 2012年07月 [査読有り][通常論文]
     
    Density functional theory (DFT) calculation was applied to acetylene (AC) and 2-butyne-1,4-diol (BD) adsorbed on an Ni(1 1 1) or Ni(1 0 0) model cluster surface in order to elucidate the relationship between their electronic states and geometry in the adsorption process. Adsorption energy of AC calculated using BSSE correction and binding structure were in good agreement with the experimental data. The geometry and adsorption energy of AC or BD on the Ni(1 1 1) surface in the optimized adsorption condition differ from those on the Ni(1 0 0) surface. Analysis of a natural electron configuration of adsorbates before and after adsorption on Ni clusters clarified that the 2s orbital rather than other orbitals such as 2p contributed mainly to the adsorption energy. (C) 2012 Elsevier B. V. All rights reserved.
  • Shigeaki Abe, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 51 1 2012年01月 [査読有り][通常論文]
     
    Density functional theory (DFT) calculations have been applied to complexes composed of ethylene carbonate (EC) with a graphene chip to theoretically elucidate the interaction of EC with the graphene. A graphene chip consisting of 14 benzene rings and one EC molecule were examined as the interaction system. Ten binding sites of EC were examined as binding e points around the graphene chip. EC binds to a hexagonal position corresponding to the central of benzene ring of graphene surface. In addition, EC can bind to the edge region of graphene. The energy of EC in the edge region was 4.2 kcal/mol more stable than that of the hexagonal position. The activation barriers for diffusion of EC on the graphene surface were significantly low (less than 0.2 kcal/mol), indicating that EC, put on the surface, can move freely on the graphene surface and then down into the edge region. (C) 2012 The Japan Society of Applied Physics
  • Tetsuji Iyama, Shigeaki Abe, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 567 200 - 206 2012年 [査読有り][通常論文]
     
    The radical addition to the smallest fullerene C-20 has been investigated by means of density functional theory (DFT) method in order to elucidate the radical scavenge mechanism of fullerene. The OH radical was examined as an organic radical because the radical has a high reactivity. The DFT calculation showed that the OH radical binds directly to the carbon atom of C-20 and a strong C-O bond is formed. The binding energies of the first addition of OH radical were calculated to be 85.2 kcal/mol at the B3LYP/6-311G(d,p) level of theory. In the second radical addition, the binding energy of OH to C-20(OH) was 91.5 kcal/mol. The unpaired electron was distributed widely over the C-20 surface in the C-20(OH) complex.
  • Hiroto Tachikawa
    RSC ADVANCES 2 17 6897 - 6904 2012年 [査読有り][通常論文]
     
    The ionization dynamics of a benzene dimer have been investigated by means of a direct ab initio molecular dynamics (MD) method in order to elucidate the reaction mechanism. Following the ionization, the T-shaped neutral benzene dimer was gradually changed to a p-stacked benzene dimer cation. The structural change and time evolution of the electronic absorption spectrum were completely visualized for the first time. The time scale of the dimer formation was estimated to be 1.0-1.5 ps. First, the benzene molecule at the stem position (Bz(')) was ionized, and the structure of Bz'(+) was rapidly deformed due to the Jahn-Teller effects. Next, the rotation of (Bz')(+) gradually occurred relative to Bz. Finally, a pi-stacked benzene dimer cation was formed. TD-DFT calculations indicated that the absorption spectrum of (Bz)(2)(+) is blue-shifted as a function of time. The formation mechanism of the benzene dimer cation was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    RSC ADVANCES 2 32 12346 - 12354 2012年 [査読有り][通常論文]
     
    Direct ab initio molecular dynamics (MD) has been applied to the electron detachment dynamics of Cu-(H2O)(n) (n = 1-3). The initial structures of Cu(H2O)(n) were generated randomly around the equilibrium point of anionic complex Cu-(H2O)(n) and then trajectories were run from the vertical electron detachment points of Cu-(H2O)(n). It was found that three reaction channels compete with each other when n = 1: dissociation channel (the product is Cu + H2O) and complex formation channel (the product is neutral CuH2O complex). The complex channel is further classified to two kind of complexes: a strongly bound (I) complex and a weakly bound (II) complex. The dissociation channel occurred from an inner Franck-Condon (FC) region where the distance Cu--H2O is shorter than the equilibrium point. On the other hand, the complex formation channel occurred from the wide FC region. In case of n = 2 and 3, dissociation channels were the main products. The mechanism of the electron detachment dynamics was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 44 20 2011年10月 [査読有り][通常論文]
     
    Structures and electronic states of graphene flakes (finite and small sized graphenes) have been investigated by means of the density functional theory method. Sizes of graphene flakes examined in this study were n = 7, 10, 14, 19, 29 and 44, where n is the number of benzene rings in the graphene flake. The excitation energies of graphene flakes decreased gradually as a function of the number of the ring (n). The orbitals of the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) are localized in the edge region of the graphene flake. It was found that the edge region can react with a water molecule and H2O is dissociated into OH radical and hydrogen atom (H) without an activation barrier. A lithium ion can bind strongly to the edge region. The ability of the edge region in the graphene flakes was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 115 42 20406 - 20411 2011年10月 [査読有り][通常論文]
     
    The interaction of the Li+ ion with fullerene (C-60) surface has been investigated by means of density functional theory (DFT) and direct molecular orbital-molecular dynamics (MO-MD) methods. It was found that the Li+ ion can bind two stable binding sites, hexagonal and pentagonal sites where Li+ binds to six- and five-membered rings composed of carbon atoms, respectively. The saddle points between binding sites were found: activation energies for (5-6) and (6-6) saddle points were calculated to be 2.7 and 3.6 kcal/mol at the B3LYP/6-311G(d,p) level, respectively, where (5-6) means a saddle point between pentagonal and hexagonal sites. The dynamics calculations showed that the Li+ ion diffuses between stable points near the saddle points at 250 K. The electronic states of Li+ ion along the diffusion path on C-60 were discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    CHEMICAL PHYSICS LETTERS 513 1-3 94 - 98 2011年09月 [査読有り][通常論文]
     
    Density functional theory (DFT) and direct ab initio molecular dynamics (MD) calculations have been applied to a hydrogen atom trapped in diamond cluster. The DFT calculation showed that spin density of hydrogen atom in diamond (hyperfine coupling constant, hfcc) is lower than that of free hydrogen atom in vacuo. This result was in good agreement with that of muon-spin-rotation experiment. The MD calculation showed that the hfcc of hydrogen atom decreases with increasing temperature because the hydrogen atom behaves as electron donor in diamond lattice. The electronic states of hydrogen atom trapped in the diamond were discussed on the basis of theoretical results. (C) 2011 Elsevier B. V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 115 33 9091 - 9096 2011年08月 [査読有り][通常論文]
     
    Electron capture dynamics of SO2-H2O (Ar)(n) complexes (n = 0-2) have been investigated by means of direct ab initio molecular dynamics (MD) method in order to elucidate the effects of solvent argon on the reaction dynamics of SO2-H2O. The neutral complex of SO2-H2O has a C-s symmetry, and the sulfur of SO2 interacts with the oxygen of H2O with an eclipsed form. In the SO2-H2O(Ar)(n) complexes, the dipole of H2O interacts with the argon atoms in the most stable structure. Following the electron capture of the complex SO2-H2O, the complex anion SO2-(H2O) is dissociated directly into SO2- + H2O. On the other hand, the electron capture of SO2(H2O)(Ar)(n) argon complex (n = 1-2) leads to the anion-water complex SO2- (H2O) because the collision of H2O with the Ar atom causes a rebound of H2O from Ar atom to the SO2- anion. The argon solvent enhanced the SO2-(H2O) complex formation. The reaction mechanism of SO2(H2O) in the participation of argon atoms was discussed on the basis of the present results.
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    COMPUTATIONAL MATERIALS SCIENCE 50 9 2640 - 2643 2011年07月 [査読有り][通常論文]
     
    The evaporation processes of water molecules adsorbed in the edge region of graphene have been investigated by means of direct MO-MD method. A large system composed of 29 water molecules and a graphene sheet (C(96)H(24)) was used as a model system. The edge carbon atom of graphene was terminated by hydrogen atom. The geometry optimization showed that the water molecules interact with the hydrogen atoms in the edge region of graphene. At low temperature (300 K), the water molecules were dissociated as water clusters from the graphene. On the other hand, in addition to the dissociation of water clusters, the isolated water molecule was also found as dissociation product at high temperature (500 K). The mechanism of water evaporation was discussed on the basis of theoretical results. (C) 2011 Elsevier By. All rights reserved.
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 1 2011年01月 [査読有り][通常論文]
     
    The structures and electronic states of graphene-water interaction systems have been investigated by means of density functional theory (DFT) method to elucidate the effects of water clusters on the electronic states of graphene chip. Solvation caused by five to eight water molecules (n = 5-8) was examined as the interaction systems. A graphene chip composed of 14 benzene rings was used as a model of finite-sized graphene (C42H16). The water clusters interact with the graphene chip with hydrogen bonds. The band gap of graphene was slightly red-shifted by the solvation and the first excitation energy was saturated around n = 5. The electronic states of graphene-water systems were discussed on the basis of theoretical results. (c) 2011 The Japan Society of Applied Physics
  • Shigeaki Abe, Rika Komine, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 538 258 - 264 2011年 [査読有り][通常論文]
     
    The interaction of carbon nanotubes (CNTs) and peptide molecule has been investigated by means of experiment and theoretical calculations. For comparison, the graphene-peptide system was investigated with the same manner. It was found that peptide interacts strongly with the CNTs, whereas the interaction of graphene with the peptide is negligibly small. The theoretical calculation supports strongly these findings.
  • Yoshimichi Ami, Hiroto Tachikawa, Naoki Takano, Norihisa Miki
    JOURNAL OF MICRO-NANOLITHOGRAPHY MEMS AND MOEMS 10 1 2011年01月 [査読有り][通常論文]
     
    We demonstrate the fabrication of polymer microneedle arrays using soft lithography. A photomask was designed to use Fresnel diffraction of UV light to create sharp, tapered hollows in SU-8, a negative photoresist, after development. Polymer microneedles were formed using these SU-8 structures as a mold. These polymer needles may be applicable as flexible electrodes in brain-machine interfaces because they are more likely to survive movement of the skin than conventional brittle silicon needles. Similar needles, made from medicinal substances, could be used for transdermal drug administration. For these applications, the needles must be long, sharp, and stiff enough to penetrate the stratum corneum (similar to 20 mu m in thickness) and reach the viable epidermis (200-300 mu m in thickness), but must not reach the dermis, which contains sensitive nerve endings. We successfully manufactured 20x20 microneedle arrays of polydimethylsiloxane with a needle length of 200 mu m. We experimentally verified that these manufactured electrodes successfully penetrated the stratum corneum of a cultured skin. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.3553393]
  • Takahiro Fukuzumi, Hiroto Tachikawa, Kazuhisa Azumi
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 538 61 - 66 2011年 [査読有り][通常論文]
     
    The binding structures and electronic states of sodium ion and atom (Na(+) and Na) trapped on the smallest fullerene surface (C(20)) have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of interaction. It was found that the Na(+) ion can bind two sites of C(20): one is on-top site where Na(+) ion binds to the carbon atom of C(20), while the other is a pentagonal site where the Na(+) ion binds to five membered ring of C(20). In case of sodium atom, the similar binding structures were obtained on C(20) surface. The nature of the interaction between Na(+) (Na) and the C(20) cluster was discussed on the basis of theoretical results.
  • Koichi Kato, Tetsuji Iyama, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 1 2011年01月 [査読有り][通常論文]
     
    The interaction of magnesium atom (Mg) and ionic species (Mg+ and Mg2+) with graphene chip (finite sized graphene) have been investigated by means of density functional theory (DFT) method. The B3LYP/6-31G(d) calculation showed that the Mg atom does not make a chemical bind to the graphene chip. On the other hand, the ionic species can bind srongly to a hexagonal site of graphene chip. Time-dependent (TD)-DFT calculation of Mg+ doped graphene showed that the first excitation band is assigned to a charge transfer band from a pi-orbital of graphene chip (HOMO: highest occupied molecular orbital) to a singly occupied molecular orbital (SOMO) composed of Mg+(3s) orbital, whereas the second excitation band is composed of a pi-pi(center dot) transition corresponding to the HOMO-lowest unoccupied molecular orbital (LUMO) excitation of free graphene chip. The nature of the interaction between the Mg ions and the graphene chip was discussed on the basis of theoretical results. (c) 2011 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Hiroshi Kawabata
    THEORETICAL CHEMISTRY ACCOUNTS 128 2 207 - 213 2011年01月 [査読有り][通常論文]
     
    Solvent re-orientation process of triplet acetone/methanol complex and intermolecular hydrogen atom abstraction reaction on the triplet state energy surface, (CH3)(2)C=O (T-1) + CH3OH -> (CH3)(2)C-OH + CH2OH in gas phase, have been investigated by means of density functional theory (DFT) and direct ab initio molecular dynamics (MD) methods. The static DFT calculation of hydrogen abstraction reaction at the T-1 state showed that the transition state is 16.4 and 30.9 kcal/mol lower than the energy levels of S-1 and S-2 states, respectively, and 9.2 kcal/mol higher than the bottom of T-1 state. The product state, (CH3)(2)C-OH center dot center dot center dot CH2OH, is 8.4 kcal/mol lower in energy than the level of T-1 state. The direct ab initio MD calculation showed that the product is rapidly formed within 150 fs and the separated products (CH3)(2)C-OH + CH2OH were formed. The mechanism of reaction dynamics of the triplet acetone/methanol complex was discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama, Kazuhisa Azumi
    JAPANESE JOURNAL OF APPLIED PHYSICS 50 1 2011年01月 [査読有り][通常論文]
     
    The structures and electronic states of boron- and nitrogen-substituted graphene chips ( B-, N-, and BN-doped graphene chips) have been investigated by means of the density functional theory (DFT) method in order to shed light on the mechanism of change in the electronic properties of graphene chips caused by heteroatoms. The atomic charge of nitrogen atoms in N- graphene was a negative value, whereas that of boron atoms in B-graphene was positive. In the case of the BN-doped graphene chip, a charge polarization such as B delta+-N delta- was found. It was also found that the B-N bond pair is preferentially formed because of the large heat of formation of the B-N bond. The BN-doped graphene chips showed a large red shift of the band gap compared with that of normal graphene. The electric states of BN-graphenes were discussed on the basis of theoretical results. (c) 2011 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Takahiro Fukuzumi
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 13 5881 - 5887 2011年 [査読有り][通常論文]
     
    The ionization dynamics of an aminopyridine dimer (AP)(2) has been investigated by means of the direct ab initio molecular dynamics (MD) method. It was found that the reaction process was composed of three steps after the vertical ionization of (AP)(2): dimer approach, proton transfer and energy relaxation. The timescales of these processes were 50-100, 10-20, and 200 fs, respectively. The timescale of the dimer approach was dependent on the initial separation between AP(+) and AP. After the ionization, AP approached gradually the ionized AP(+). The proton of AP(+) was transferred to AP at the nearest intermolecular distance, while the potential energy was quickly dropped according to the proton transfer. The energy relaxation of the dimer cation was significantly faster than that of the monomer cation. The mechanism of ionization dynamics of (AP)(2) was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 23 11206 - 11212 2011年 [査読有り][通常論文]
     
    Ionization dynamics of a water dimer have been investigated by means of a direct ab initio molecular dynamics (MD) method. Two electronic state potential energy surfaces of (H2O)(2)(+) (ground and first excited states, (2)A '' and (2)A') were examined as cationic states of (H2O)(2)(+). Three intermediate complexes were found as product channels. One is a proton transfer channel where a proton of H2O+ is transferred into the H2O and then a complex composed of H3O+(OH)was formed. The second is a face-to-face complex channel denoted by (H2O-OH2)(+) where the oxygen-oxygen atoms directly bind each other. Both water molecules are equivalent to each other. The third one is a dynamical complex where H2O+ and H2O interact weakly and vibrate largely with a large intermolecular amplitude motion. The dynamics calculations showed that in the ionization to the (2)A '' state, a proton transfer complex H3O+(OH) is only formed as a long-lived complex. On the other hand, in the ionization to the (2)A' state, two complexes, the face-to-face and dynamical complexes, were found as product channels. The proton of H2O+ was transferred to H2O within 25-50 fs at the (2)A '' state, meaning that the proton transfer on the ground state is a very fast process. On the other hand, the decay process on the first excited state is a slow process due to the molecular rotation. The mechanism of the ionization dynamics of (H2O)(2) was discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Akihiro Yabushita, Masahiro Kawasaki
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 13 46 20745 - 20749 2011年 [査読有り][通常論文]
     
    A direct ab initio molecular dynamics method has been applied to a water monomer and water clusters (H2O)(n) (n = 1-3) to elucidate the effects of zero-point energy (ZPE) vibration on the absorption spectra of water clusters. Static ab initio calculations without ZPE showed that the first electronic transitions of (H2O)(n), B-1(1) <- (1)A(1), are blue-shifted as a function of cluster size (n): 7.38 eV (n = 1), 7.58 eV (n = 2) and 8.01 eV (n = 3). The inclusion of the ZPE vibration strongly affects the excitation energies of a water dimer, and a long red-tail appears in the range of 6.42-6.90 eV due to the structural flexibility of a water dimer. The ultraviolet photodissociation of water clusters and water ice surfaces is relevant to these results.
  • Hiroto Tachikawa, Tetsuji Iyama, Shigeaki Abe
    9TH INTERNATIONAL CONFERENCE ON NANO-MOLECULAR ELECTRONICS 14 2011年 [査読有り][通常論文]
     
    The interaction of OH radical with C-60 has been investigated by means of DFT method in order to elucidate the radical scavenge mechanism of fullerene. The OH radical was examined as an organic radical because the radical has a high reactivity. The DFT calculation showed that the OH radical binds to the carbon atom of C-60 and a strong C-O bond is formed. The binding energies were calculated to be 36.4 and 35.2 kcal/mol at the B3LYP/6-31G(d) and 6-311G(d,p) levels of theory. The potential energy curve plotted as a function of C-O distance showed that the OH radical approaches to the carbon atom without activation barrier. Also, it was found that structural change from sp(2) to sp(3)-like hybridization occurs easily by the approach of OH. The unpaired electron is distributed widely over the C-60 surface in the C-60(OH) complex. (C) 2010 Published by Elsevier B.V.
  • Takeshi Sakamoto, Kazuhisa Azumi, Hiroto Tachikawa, Kei Iokibe, Masahiro Seo, Nobuya Uchida, Yasunaga Kagaya
    ELECTROCHIMICA ACTA 55 28 8570 - 8578 2010年12月 [査読有り][通常論文]
     
    Structures of Ni films electrodeposited from a Watts-type bath containing 2-buthyne-1 4-diol (BD) were investigated using SEM cross-sectional SIM XRD measurement with a pole profiling technique and electrochemical methods for controlling properties of Ni electrodeposits Preferred orientation of Ni electrodeposits was assigned to potential domains for electrodeposition Preferred orientation in the higher potential region was (1 1 0) or (1 00) that in the middle potential region were (1 1 1) and (3 1 1) and that in the lower potential region was (1 0 0) The growing axis of Ni electrodeposits seems to agree with the speculation from Pangarov s model based on the two-dimensional nuclei theory in the lower overpotential region in which the dominant growing plane is fundamentally determined by crystallization overpotential related to supersaturation of adatom although the growth axes of Ni deposits do not always agree with the preferred orientation For example preferred orientation of (1 1 0) was assigned to growing (1 1 1) plane which tilts at 55 degrees to the substrate Adsorption of BD affects the structure and morphology of electrodeposits via an inhibitory effect related to its surface coverage depending on surface orientation growth rate and BD concentration in the plating bath (C) 2010 Elsevier Ltd All rights reserved
  • Hiroto Tachikawa, Takahiro Fukuzumi, Kazushige Inaoka, Inosuke Koyano
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 47 15399 - 15405 2010年12月 [査読有り][通常論文]
     
    The ion-molecule reaction, CH3CN+ + CH3CN -> CH3CNH+ + CH2CN, has been investigated using the threshold electron-secondary ion coincidence (TESICO) technique. Relative reaction cross sections for two microscopic reaction mechanisms, i.e., proton transfer (PT) from the acetonitrile ion CH3CN+ to neutral acetonitrile CH3CN and hydrogen atom abstraction (HA) by CH3CN+ from CH3CN, have been determined for two low-lying electronic states, E-2 and (2)A(1) of the CH3CN+ primary ion. The cross section for PT of the (2)A(1) state was smaller than that of the E-2 state, whereas that of HA are almost the same in the two states. Ab initio calculations showed that the dissociation of the C-H+ bond of CH3CN+ is easier in the E-2 state than that in the (2)A(1) state. The direct ab initio molecular dynamics (MD) calculations showed that two mechanisms, direct proton transfer and complex formation, contribute the reaction dynamics.
  • Hiroto Tachikawa, Yoshinori Nagoya, Takahiro Fukuzumi
    JOURNAL OF POWER SOURCES 195 18 6148 - 6152 2010年09月 [査読有り][通常論文]
     
    The electronic structures of a lithium ion (Li+) doped-graphene at the ground and low-lying excited states have been investigated by means of density functional theory (DFT) method. A graphene composed of 19 benzene rings was used as a model of graphene, while the edge carbon atom was terminated by hydrogen atom (expressed by C54H18). The geometry optimization showed that the Li+ ion binds to a hexagonal site where six carbon atoms interact equivalently to the Li+ ion. When the Li+ ion interacts with the graphene surface, the electronic configuration of the Li+ ion is changed from (1s)(2)(2s)(0) to (1s)(2)(2s)(0.01)(2p)(0)(3p)(0.02), suggesting that the sp-hybridization of lithium ion is important in the adsorption to the graphene surface. The band gap of graphene is slightly red-shifted by the doping of Li+ ion due to the interaction with the sp-hybrid orbital. The effects of Li+ on both the ground and excited electronic states of graphene were discussed on the basis of theoretical results. (C) 2010 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 114 37 10309 - 10314 2010年09月 [査読有り][通常論文]
     
    Electron capture dynamics of the water tetramer (H2O)(n) (n = 4) have been investigated by means of a full-dimensional direct ab initio molecular dynamics (MD) method at the MP2/6-311++G(d,p) level. Two structural conformers (branched and cyclic forms of the water tetramer) were examined as neutral water tetramers. The structure of the branched form is that a dangling water molecule binds to the ring composed of a cyclic water trimer. In the case of electron capture of the branched form, first, an excess electron was trapped by the dangling water molecule. Next, rotation of the water molecule located in the ring occurred rapidly, while a hydrogen bond of the ring was broken. The branched structure was gradually changed to a linear one. This change was caused by the increase of the dipole moment of the neutral water tetramer oriented toward the excess electron. The time scale of hydrogen bond breaking and solvation of the excess electron were estimated to be 100 and 400 fs, respectively. In the case of the cyclic water tetramer, a planar structure was only changed to a slight bent form. The mechanism of electron capture of the water tetramer (mainly the branched form) was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 114 14 4951 - 4956 2010年04月 [査読有り][通常論文]
     
    The electron capture dynamics of hydroperoxy radical-water complexes have been investigated by means of direct density functional theory (DFT) molecular dynamics (MD) method to elucidate the solvation (hydration) effect on the reaction mechanism. The complexes composed of HOO and one to four water molecules, HOO(H2O)(n) (n = 1-4), were considered to be the hydrated HOO system. After the electron capture of n = 1, only solvent reorientation of H2O around HOO- occurred, and a stable complex (HOO--H2O) was formed within 100-300 fs. In the case of n = 2-4, a proton of H2O was transferred from H2O to OOH-, whereas H2O2 and OH-(H2O)(n-1) were found as products. It was suggested that the MOO radical adsorbed on water cluster is efficiently converted in the H2O2 without activation barrier after the electron capture of HOO. Time scales of proton transfer were calculated to be 200-300 fs. The mechanism of electron capture of HOO in polar stratospheric cloud was discussed on the basis of theoretical results.
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 6 2010年 [査読有り][通常論文]
     
    Effects of water molecules on the electronic states of graphene have been investigated by means of density functional theory (DFT) and time-dependent DFT methods at the PW91PW91 and B3LYP/6-31G(d) levels of theory. Solvation caused by one to four water molecules (n = 1-4) was examined in the present study. A graphene composed of 14 benzene rings was used as a model of finite-sized graphene (C42H16). The water molecules interact with the graphene surface via hydrogen bonding. The band gap of graphene was slightly red-shifted by the solvation. This shift was caused by the formation of hydrogen bonds between H2O and the graphene surface. The electronic states of the graphene-water system were discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Shigeaki Abe, Yoshinori Nagoya, Fumio Watari, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    The evaporation processes of water from the edge region of graphene sheets was investigated by means of the direct molecular orbital-molecular dynamics (MO-MD) method at the AM1 level. Five graphenes with n = 1, 7, 19, 37, and 61 (where n is the number of benzene rings in the graphene) were examined as models of graphene sheets. The edge carbons of each graphene were terminated by hydrogen atoms. In the H2O-graphene interaction system, the oxygen atom of the water molecule binds to one or two C-H hydrogen atoms of the edge carbons. The binding energy of H2O increased gradually as a function of n and was saturated around n = 61. At low temperature (10-100 K), the water molecule was still connected to the graphene sheet, whereas the evaporation of H2O was found above 300 K. The mechanism of water evaporation is discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY 40 5 306 - 311 2010年 [査読有り][通常論文]
     
    Effects of point charges on the excitation energies of protonated Schiff base of retinal (PSBR) in gas phase have been investigated by means of time-dependent density functional theory (TD-DFT) method in order to shed light on the electrostatic effects on the absorption spectra of PSBR. The positive and negative charges around PSBR were tested for 11-cis of PSBR. The TD-DFT calculations indicated that the first and second excitation energies are blue-shifted by the existence of the negative charge around the N-H site of PSBR, whereas those are red-shifted by positive charge. On the other hand, the spectral feature in -ionone ring was much different from that of the N-H site: the first and second excitation energies are red-shifted by the negative charge. The spectral feature is drastically changed at the polyene part of PSBR. It was found that the excitation energies of PSBR are affected strongly by the electrostatic environment. The effects of electrostatic interaction on the absorption spectra of PSBR are discussed on the basis of theoretical results.
  • Shigekazu Ohmori, Hiroshi Kawabatay, Ken Tokunaga, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    The electronic structure and density distribution in the poly-fused furans were investigated using density functional theory (DFT) calculations. Differential electron density (DED) distribution analysis of the neutral and charged states of oligomer species were calculated to visualize spatial charge modulation in the molecular. Polymers of fused furans [p-F(n)] were also investigated using one-dimensional periodic boundary conditions (PBC) for comparison. A difference in the electronic structure and density distribution of p-F(n) was found between electron and hole transport processes. The electronic states of F(n) and p-F(n) were discussed on the basis of the differential electron density distribution, density of states (DOS) around the frontier states, and crystal orbital overlap population (COOP) analysis. (C) 2010 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Shigeaki Abe
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 12 15 3904 - 3909 2010年 [査読有り][通常論文]
     
    Structures and electronic states of the HOO radical interacting with water molecules, expressed by HOO(H2O)(n) (n = 1 and 2), have been investigated by means of a direct ab initio molecular dynamics (MD) method. From the static ab initio calculation of HOO-H2O complex, two types of HOO radical were found: i.e., the HOO radical acts as a hydrogen donor or acceptor in the complex (n = 1). The binding energies of former and latter complexes were calculated to be 8.7 and 3.3 kcal mol(-1), respectively, at the QCISD/6-311 + + G(2d, 2p) level. In the case of 1 : 2 complex HOO(H2O)(2), a cyclic structure with a hydrogen donor of HOO was obtained as the stable form. Effects of zero point vibration on the structures and hyperfine coupling constants of the HOO radical were also investigated. The structures and electronic states of HOO(H2O)(n) (n = 1 and 2) were discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 6 2010年 [査読有り][通常論文]
     
    The structures and electronic states of hydrogenated graphenes with a finite size have been investigated by a density functional theory (DFT) method. Five graphenes of various sizes (n = 2, 4, 7, 14, and 19, where n indicates the number of benzene rings in graphene) were examined as models of a hydrogenated graphene system. The harmonic vibrational frequency corresponding to a C-H stretching mode showed a linear relationship between the frequency and the C-H bond length. The C-H bond formed by the addition of hydrogen atoms was completely polarized as C delta--H delta+ in an equilibrium structure. It was found that the activation barrier is formed by hybridization from sp(2) to sp(3) in the transition region. The mechanism of C-H bond formation on a graphene surface was discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    Direct molecular orbital-molecular dynamics (MO-MD) method has been applied to diffusion processes of the Li+ ion on a modified graphene surface. A graphene sheet composed of carbon, fluorine and hydrogen atoms were used as a model graphene (Li+C150H3F27, denoted by FH-graphene). The edges of graphene were terminated by fluorine (F-edge region) and hydrogen atom (H-edge region). Simulation temperatures were chosen in the range 250-350 K. It was found that the lithium ion diffuses freely on the surface, but the ion does not approach the F-edge region of the surface. This is due to the repulsive interaction with a positive charged carbon atom where C-F bond is polarized as C delta+-F delta-. On the other hand, the Li+ ion approached to the H-edge region and it exited from the H-edge region. The diffusion mechanism of Li-was discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    JAPANESE JOURNAL OF APPLIED PHYSICS 49 1 2010年 [査読有り][通常論文]
     
    Geometrical and electronic structures of a hydrogen-added graphene have been investigated by means of density functional theory (DFT) and direct molecular dynamics (MD) methods. A graphene composed of 19 benzene rings was examined as a model of finite-sized graphene. The hyperfine coupling constants (hfcc's) of hydrogen atoms on graphene were calculated to be similar to 63 G in the bulk region and 20-5 G in the edge region of graphene, indicating that the hfcc of hydrogen atoms is strongly dependent on the bonding site. The excitation energies of hydrogen added graphene were calculated to be 1.28, 1.54, and 1.60 eV, which were lower than that of graphene without hydrogen atoms (2.24 eV). The first electronic transition was assigned to an excess electron transfer band from a defect hydrogen site to the bulk region of graphene. The electronic states and thermal behavior of hydrogen atoms interacting with graphene are discussed on the basis of theoretical results. (C) 2010 The Japan Society of Applied Physics
  • Shigekazu Ohmori, Hiroshi Kawabata, Ken Tokunaga, Hiroto Tachikawa
    THIN SOLID FILMS 518 2 901 - 905 2009年11月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for oligomer species of a fused porphyrin, denoted by P(n), where n represents the number of porphyrin rings in the oligomer, to elucidate the electronic structures at ground and excited states. A polymer of fused porphyrin (p-Por) was also investigated using one-dimensional periodic boundary conditions (PBC) for comparison. It was found that the lowest energy band is located below 0.6 eV in the case of oligomers larger than n = 8, which corresponds to a band gap of p-Por. Carrier transport pathways in p-Por were discussed on the basis of theoretical results. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    THIN SOLID FILMS 518 2 877 - 879 2009年11月 [査読有り][通常論文]
     
    The interaction of magnesium (Mg) with a graphene surface has been investigated by means of density functional theory (DFT) method. Also, the direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa, J. Phys. Chem. C, 112 (2008) 101931 have been applied to the dynamics of Mg on the graphene surface. The B3LYP/LANL2MB calculations showed that the Mg atom is bound to a hexagonal site and is located in 2.02 angstrom from the graphene surface. The direct MO-MD calculations showed that the Mg atom vibrates in the hexagonal site and diffusion does not occur even at 1000 K. The nature of the interaction between the Mg atom and the graphene sheet was discussed on the basis of theoretical results. (C) 2009 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    THIN SOLID FILMS 518 2 873 - 876 2009年11月 [査読有り][通常論文]
     
    The structures and electronic states of sodium ion (Na(+)) trapped on the graphene have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of interaction between Na(+) and the graphenes. In addition, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa, J. Phys. Chem. C, 112 (2008) 101931 was applied to diffusion processes of the Na(+) ion on graphene. The graphene composed of 37 benzene rings was used as a model of graphene. The B3LYP/LANL2MB calculation showed that the sodium ion is stabilized in hexagonal site and is located at ca. 2.230 angstrom from the graphene surfaces. The direct MO-MD calculation showed that the Na(+) ion diffuses freely on the graphene surface, but the ion did not approach the edge region due to the fact that a high potential barrier exists near the edge region. The nature of interaction between Na(+) and graphene was discussed on the basis of theoretical results. (C) 2009 Elsevier B.V. All rights reserved.
  • Tomoya Takada, Hiroto Tachikawa
    JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL 311 1-2 54 - 60 2009年09月 [査読有り][通常論文]
     
    Methyl radicals interacting with silica gel surfaces have been investigated by means of DFT and direct ab-initio molecular dynamics (MD) methods using cluster models. Four typical binding sites of CH3 on the cluster models were found in the geometry optimization from several initial geometries of CH3 around the silica gel clusters. These were two silanol Si-OH sites and two siloxane Si-O-Si sites. In both sites, magnitude of hyperfine coupling constants of the methyl radical (a(H)) was smaller than that of free CH3 (a(H) = 23.04 G). Temperature effects on aH of the methyl radical were investigated by means of the direct ab-initio MD method. The hyperfine coupling constant of CH3 interacting with the SiOH group decreased with increasing temperature. The methyl radical interacting with alkali metal supported silica gel was also investigated for comparison. The electronic states of methyl radicals on silica gel were discussed on the basis of theoretical results. (C) 2009 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Yoshinori Nagoya, Hiroshi Kawabata
    JOURNAL OF CHEMICAL THEORY AND COMPUTATION 5 8 2101 - 2107 2009年08月 [査読有り][通常論文]
     
    Electronic states of graphenes, whose carbon atoms are terminated by hydrogen atoms (hydrogenated graphene, denoted H-graphene) and defective graphene (one carbon atom was removed from H-graphene, denoted D-graphene) have been investigated by density functional theory. The sizes of graphenes examined in the present study were n = 7, 14, 19, 29, 37, 44, and 52; where n is the number of benzene rings in the graphene. The excitation energies of H-graphenes were gradually decreased as a function of the number of rings. In D-graphene, new energy levels for the first and second excited states appeared as low-lying excited states. It was found that the formation of defect sites in graphene produces large decreases in the excitation energies for third and higher excited states. The highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO) in H-graphene were widely delocalized over the graphene surface. On the other hand, LUMO in D-graphene was localized only in the defect sites. The effects of vacancy defects on both the ground and excited electronic states of graphene were discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY C 113 18 7603 - 7609 2009年05月 [査読有り][通常論文]
     
    Electronic states of normal graphene, the defective graphene (one carbon atom is removed from the normal graphene), the defective graphene anion (defective graphene plus an excess electron), and the defective graphene cation (defective graphene plus one hole) have been investigated by means of density functional theory (DFT) and direct molecular orbital-molecular dynamics (MO-MD) methods in order to elucidate the effect of vacancy defect on the electronic states of graphene. The HOMO and LUMO of normal graphene were widely delocalized as pi-conjugated orbitals over the graphene surface in the normal graphene. On the other hand, the excess electron in defective graphene anion was localized in the defect site, indicating that the excess electron on the graphene circuit is,efficiently trapped and stabilized by the vacancy defect site of graphene. The direct MO-MD calculations showed that the trapped electron in the defect site is stable at low temperature. Around room temperature (300 K), the structural change of the graphene backbone was found and the vacancy defect was reconstructed by thermal activation. The excess electron escaped from the defect site of the reconstructed graphene, while the spin density delocalized the graphene.
  • Tetsuji Iyama, Kohichi Kato, Hiroshi Kawabata, Hiroto Tachikawa, Kazuhisa Azumi
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 504 140 - 146 2009年 [査読有り][通常論文]
     
    The structures and electronic states of sodium atom (Na) trapped on the graphene surfaces have been investigated by means of density functional theory (DFT) calculation to elucidate the nature of interaction between Na and the graphenes. In addition, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa, J. Phys. Chem. C, 112 (2008) 10193] was applied to diffusion processes of the Na atom on graphene surfaces. Seven graphenes (n = 7, 14, 19, 29, 37, 44 and 52, where n means numbers of rings in each carbon cluster) were examined in the present study. The B3LYP/LANL2MB calculation showed that the sodium atom is located at ca. 3.0 angstrom from the graphene surfaces. The direct MO-MD calculation showed that diffusion of Na atom is slower than that of Na+ ion on graphene surface. The nature of the interaction between Na atom and the carbon clusters was discussed on the basis of theoretical results.
  • Hiroshi Kawabata, Tetsuji Iyama, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 504 147 - 154 2009年 [査読有り][通常論文]
     
    Electronic states of lithium ion (Li+) interacting with a chlorinated graphene surface (Cl- graphene) have been investigated by means of hybrid density functional theory (DFT) to elucidate the effect of chlorination of graphene on the diffusion of lithium ion. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [H. Tachikawa, J. Phys. Chem. C, 112 (2008) 10193] was applied to diffusion processes of the Li+ ion on Cl- graphene. The potential barrier height for movement of Li+ was estimated to be 2.95 kcal/mol on Cl- graphene. The direct MO-MD calculations showed that the Li+ ion diffuses freely on bulk and edge region of Cl- graphene at 300 K. The nature of the interaction between Li+ and Cl- graphene was discussed on the basis of theoretical results.
  • SN2反応を実時間で見る!
    化学 64 62 - 63 2009年 [査読無し][通常論文]
  • Yasunori Yamamoto, Shingo Takada, Norio Miyaura, Tetsuji Iyama, Hiroto Tachikawa
    ORGANOMETALLICS 28 1 152 - 160 2009年01月 [査読有り][通常論文]
     
    Cross-coupling between bromoarenes and [(E)-CH3CH=CHCH2BF3]K (2a) by a catalyst prepared from Pd(OAc)(2) and D-t-BPF selectively provided gamma-coupling products via S(E)2' substitution. Mechanistic study of transmetalation revealed a heretofore unknown process, namely, formation of a highly electrophilic [Pd(Ar)(D-t-BPF)](+) before transmetalation with 2a. Thus, kinetic data in coupling of 4-substituted bromoarenes with 2a showed a linear positive correlation (rho = -1.1) accelerated by donating substituents. This rate-determining role of transmetalation was further confirmed by kinetic data between oxidative adducts [Pd(Ar)(Br)(D-t-BPF)] and 2a that exhibited an analogous correlation with a negative rho-value (-0.50). Theoretical study by density functional theory (DFT) calculation showed that transmetalation between [Ar-Pd](+) and 2a via an S(E)2' (open) transition state is a slightly lower energy process than an S(E)2' (closed) process. Allylic substitutions with chiral catalysts are the current topics for enantioselective C-C bond fort-nation, but the catalysts that are effective for allylic nucleophiles have remained unexplored. Among the ligands screened, (R,S)-CyPF-t-Bu was found to achieve 77-90% ee for representative para-and meta-substituted bromoarenes and 2-bromo-l-alkenes in refluxing aqueous tetrahydrofuran (THF) or MeOH. To obtain mechanistic information on enantioselection, the mode of substrate coordination to a cationic phenylpalladium intermediate was calculated, that is, the reaction stage directly preceding the stereodetermining insertion step by DFT calculation. A stable adduct between [Pd(CyPF-t-Bu)(Ph)](+) and 2a located at the C-C double bond from its re-face yielding the experimentally observed R-product is preferred thermodynamically rather than the corresponding si-coordination.
  • KAWABATA Hiroshi, IYAMA Tetsuji, TACHIKAWA Hiroto
    Mol. Crst. Liq. Crst. 504 147 - 154 2009年 [査読有り][通常論文]
  • Shigeaki Abe, Fumio Watari, Tomoya Takada, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 505 289 - 296 2009年 [査読有り][通常論文]
     
    The interaction of manganese (II) ion (Mn2+) with graphene surfaces have been investigated by means of density functional theory (DFT). Also, the molecular dynamics (MD) calculations using molecular mechanics-2 (MM2) potential functions have been applied to the diffusion dynamics of Mn2+ on the graphene surface. Two graphene sheets (n = 19 and 52, where n means numbers of rings in each carbon cluster) were considered as models of graphene surface in the present study. The B3LYP/LANL2MB calculations showed that the Mn2+ ion is located in the ranges 2.28-2.46 angstrom from the graphene surface. Also, classical MD calculation was applied to diffusion processes of the Mn2+ on the graphene surface (n - 52). The classical MD calculations showed that the Mn2+ ion diffuses from bulk to edge region at 300-600 K and is trapped in the edge region. The nature of the interaction between the Mn2+ ion and the graphene sheet was discussed on the basis of theoretical results.
  • IYAMA Tetsuji, KATO Kohichi, KAWABATA Hiroshi, TACHIKAWA Hiroto, AZUMI Kazuhisa
    Mol. Crst. Liq. Crst. 504 140 - 146 2009年 [査読無し][通常論文]
  • Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
    PHYSICS AND CHEMISTRY OF LIQUIDS 47 1 103 - 109 2009年 [査読有り][通常論文]
     
    Hydrogen molecules inserted into water clusters have been investigated by means of both density functional theory and ab initio calculations in order to determine a limit to the hydrogen storage capacity of water clusters. Three water clusters, (H2O)m (m = 20, 24 and 28), were examined as the water cages, while the guest hydrogen molecules up to nine were tested in the calculations. The maximum capacities of hydrogen storage for m = 20, 24 and 28 were determined to be n = 3, 6 and 8, respectively, at the MP2/6-311G(d, p)//B3LYP/6-311G(d, p) level of theory. In order to elucidate thermal behaviour of the hydrogen hydrate, direct molecular orbital-molecular dynamics calculations were carried out for (H2)n(H2O)m (n = 6 and 8, m = 28). It was found that the hydrogen molecule escapes from the hexagonal site without large deformation to the water lattice. The electronic states of the hydrogen molecules in the water clusters were discussed on the basis of theoretical results.
  • Hiroto Tachikawa, Tetsuji Iyama, Kohichi Kato
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 11 28 6008 - 6014 2009年 [査読有り][通常論文]
     
    Direct ab initio molecular dynamics (MD) method has been applied to a benzophenone-water 1 : 1 complex Bp(H(2)O) and free benzophenone (Bp) to elucidate the effects of zero-point energy (ZPE) vibration and temperature on the absorption spectra of Bp(H(2)O). The n-pi* transition of free-Bp (S(1) state) was blue-shifted by the interaction with a water molecule, whereas three pi-pi* transitions (S(2), S(3) and S(4)) were red-shifted. The effects of the ZPE vibration and temperature of Bp(H(2)O) increased the intensity of the n-pi* transition of Bp(H(2)O) and caused broadening of the pi-pi* transitions. In case of the temperature effect, the intensity of n-pi* transition increases with increasing temperature. The electronic states of Bp(H(2)O) were discussed on the basis of the theoretical results.
  • Imaging of Nucleophiric dynamics
    Chemistry 64 62 - 63 2009年 [査読無し][通常論文]
  • Hiroto Tachikawa, Andrew J. Orr-Ewing
    JOURNAL OF PHYSICAL CHEMISTRY A 112 46 11575 - 11581 2008年11月 [査読有り][通常論文]
     
    Electron capture dynamics of protonated methane (CH5+) have been investigated by means of a direct ab initio molecular dynamics (MD) method. First, the ground and two low-lying state structures of CH5+ with eclipsed C-s, staggered C-s and C-2v symmetries were examined as initial geometries in the dynamics calculation. Next, the initial structures of CH5+ in the Franck-Condon (FC) region were generated by inclusion of zero point energy and then trajectories were run from the selected points on the assumption of vertical electron capture. Two competing reaction channels were observed: CH5+ + e(-) -> CH4 + H (I) and CH5+ + e(-) -> CH3 + H-2 (II). Channel II occurred only from structures very close to the s-C-s geometry for which two protons with longer C-H distances are electronically equivalent in CH5+. These protons have the highest spin density as hydrogen atoms following vertical electron capture of CH5+ and are lost as H-2. On the other hand, channel I was formed from a wide structural region of CH5+. The mechanism of the electron capture dynamics of CH5 is discussed on the basis of the theoretical results.
  • Shinichi Enami, Yosuke Sakamoto, Takashi Yamanaka, Satoshi Hashimoto, Masahiro Kawasaki, Kenichi Tonokura, Hiroto Tachikawa
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 81 10 1250 - 1257 2008年10月 [査読有り][通常論文]
     
    The yields of IO radical from the reaction of CH3I with Cl atom in the presence of O-2 were determined as functions of total pressure from 5 to 250 Torr of N-2 diluent and temperature over the range of 278 to 328 K using cavity ring-down spectroscopy. The yields are pressure and temperature dependent. The rate constants and product branching ratios of the reaction of CH2I radical with O-2 were investigated. We determined a rate constant of (1.28 +/- 0.22) x 10(-12) cm(3) molecule(-1) s(-1) at 298 K (2 sigma uncertainty) for this reaction. Theoretical calculations were performed to determine energetics of the reactions of CH2I + O-2, and CH2Br + O-2. The present results suggest that non-negliggible IO radicals will be formed from the reactions of CH3I/CH2I2 + OH/Cl/NO3 at atmospheric conditions.
  • Hiroto Tachikawa, Hiroshi Kawabata
    CHEMICAL PHYSICS LETTERS 462 4-6 321 - 326 2008年09月 [査読有り][通常論文]
     
    DNA repair reactions of the thymine dimer ( T) 2 following the hole capture have been investigated by means of direct ab initio molecular dynamics ( MD) method in order to elucidate the mechanism of repair processes of thymine dimer interacting with a photo-enzyme. The thymine dimer has two C-C single bonds between thymine rings at neutral state expressed by (T=T). After the hole capture of (T=T), one of the C-C bonds was preferentially broken, while the structure of (T=T)(+) was spontaneously changed to an intermediate having a C-C single bond expressed by (T-T)(+). Time scale of the C-C bond breaking and formation of the intermediate was estimated to be 60-180 fs. The mechanism of repair reactions of the thymine dimer was discussed on the basis of theoretical results. (C) 2008 Elsevier B.V. All rights reserved.
  • Yukio Nakano, Hiromi Ukeguchi, Takashi Ishiwata, Yugo Kanaya, Hiroto Tachikawa, Atsushi Ikeda, Shigeyoshi Sakaki, Masahiro Kawasaki
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 81 8 938 - 946 2008年08月 [査読有り][通常論文]
     
    The rate constants of the reaction of NO3 With CH3I, which can affect iodine chemistry in the atmosphere, were measured in the temperature range of 298-323 K with cavity ring-down spectroscopy. The reaction has a rate constant of k = (4.1 +/- 0.2) x 10(-13) cm(3) molecule(-1) s(-1) at 298 K. Uncertainties reported herein are one standard deviation. On the basis of an Arrhenius plot in the region of 298-323 K, the reaction has an activation energy (E-a = 13 +/- 3 kJ mol(-1)). Density functional and coupled-cluster calculations suggest that the reaction proceeds via a transition state in which the hydrogen atom is nearly located at the middle position between the carbon atom of CH3I and the oxygen atom of NO3 to give HNO3 + CH2I. On the atmospheric implications, box model simulations indicate that the present reaction has an important effect on the levels and diurnal patterns of the mixing ratios of NO3 and CH3I, and also on the activation of iodine chemistry in the atmosphere.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 112 27 10193 - 10199 2008年07月 [査読有り][通常論文]
     
    A direct molecular orbital-molecular dynamics (MO-MD) method has been applied to diffusion processes of the Li+ ion on a fluorinated graphene surface. A graphene sheet composed Of C96F24 (denoted by F-graphene) was used as a model of the fluorinated graphene surface. The total energy and energy gradient on the full dimensional potential energy surface of the Li+C96F24 system were calculated at each time step in the trajectory calculation. The calculations were carried out at the AM I level. Simulation temperatures were chosen in the range 200-1000 K. At low temperatures, below 200 K, the diffusion of lithium ion did not occur, and the ion vibrates around an equilibrium point. At around room temperature (similar to 300 K), the lithium ion diffused freely on the surface, but the ion did not approach to the edge region of the surface. This is due to the repulsive interaction with positively charged carbon atom connecting to the fluorine atom where the C-F bond is polarized as C delta+-F delta-. The repulsive interaction strongly dominates the diffusion path of the Li+ ion on the F-graphene. However, the order of magnitude of diffusion coefficient for the Li+ ion moving on the F-graphene surface was close to that of the normal graphene surface (H-graphene). At higher temperatures, the Li+ ion moves freely on the F-graphene, and it fell in the edge region. On the basis of theoretical results, we designed a molecular device composed of F-graphite sheets.
  • Hiroshi Kawabata, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 9 2 24405 - 24411 2008年06月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation species of a fused selenophene oligomer, denoted by Se(n), where n represents the number of selenophene rings in the oligomer, to elucidate the electronic structures at ground and low-lying excited states. A polymer of fused selenophene was also investigated using one-dimensional periodic boundary conditions (PBC) for comparison. It was found that the reorganization energy of a radical cation of Se(n) from a vertical hole trapping point to its relaxed structure is significantly small. Also, the reorganization energy decreased gradually with increasing n, indicating that Se(n) has an effective intramolecular hole transport property. It was found that the radical cation species of Se(n) has a low-energy band in the near-IR region, which is strongly correlated to hole conductivity. The relationship between the electronic states and intramolecular hole conductivity was discussed on the basis of theoretical calculations.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF PHYSICAL CHEMISTRY B 112 24 7315 - 7319 2008年06月 [査読有り][通常論文]
     
    The interaction between the fully reduced flavin-adenine dinucleotide (FADH(-)) and thymine dimer (T)(2) has been investigated by means of density functional theory (DFT) calculations. The charges of FADH(-) and (T)(2) were calculated to be -0.9 and -0.1, respectively, at the ground state. By photoirradiation, an electron transfer occurred from FADH(-) to (T)(2) at the first excited state. Next, the reaction dynamics of electron capture of (T)(2) have been investigated by means of the direct ab initio molecular dynamics (MD) method (HF/3-21G(d) and B3LYP/6-31G(d) levels) in order to elucidate the mechanism of the repair process of thymine dimer caused by the photoenzyme. The thymine dimer has two C-C single bonds between thymine rings (C(5)-C(5') and C(6)-C(6') bonds) at the neutral state, which is expressed by (T)(2). After the electron capture of (T)(2), the C(5)-C(5') bond was gradually elongated and then it was preferentially broken. The time scale of the C-C bond breaking and formation of the intermediate with a single bond (T)(2)(-) was estimated to be 100-150 fs. The present calculations confirmed that the repair reaction of thymine dimer takes place efficiently via an electron-transfer process from the FADH(-) enzyme.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    THIN SOLID FILMS 516 9 2611 - 2614 2008年03月 [査読有り][通常論文]
     
    The electronic states of sodium ion (Na+) trapped on the model surfaces of amorphous carbon have been investigated by means of hybrid density functional theory (DFT) calculations to elucidate the nature of interaction between Na+/Na and the amorphous carbon surfaces. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa and Shimizu, J. Phys. Chem. 13, 110 (2006) 20445] was applied to diffusion processes of the Na+ ion on the model surface of amorphous carbon. Seven models of graphene sheets (n = 7, 14, 19, 29, 3 7, 44 and 52, where n means numbers of rings in each carbon cluster) were considered in the present study. The B3LYP/LANL2MB calculations showed that the sodium ion is located at 2.24-2.26 angstrom from the graphene surfaces. The direct MO-MD calculations showed that the Na+ ion diffuses freely on the surface above 300 K. At higher temperature (1100 K), the Na+ ion moved from the center to edge region of the model surface. The nature of the interaction between Na+ and the amorphous carbon surfaces was discussed on the basis of theoretical results. (c) 2007 Elsevier B.V. All rights reserved.
  • Hiroshi Kawabata, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    THIN SOLID FILMS 516 9 2421 - 2425 2008年03月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation of fused furan oligomer, denoted by F(n) where n means number of furan rings in the oligomer, to elucidate the electronic structures at ground and low-lying excited states. A polymer of fused furan was also investigated using one-dimensional periodic boundary condition (PBC) for comparison. It was found that the reorganization energy of radical cation of F(n) from vertical hole trapping point to its relaxed structure is significantly small. Also, the reorganization energy decreased gradually with increasing n, indicating that F(n) has an effective hole transport property. It was found that the cation radical of F(n) has a low energy band at near IR region, which is strongly correlated to hole conductivity. The relation between the electronic states and hole conductivity was discussed on the basis of theoretical calculations. (C) 2007 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    THIN SOLID FILMS 516 10 3287 - 3293 2008年03月 [査読有り][通常論文]
     
    Hybrid density functional theory calculations have been carried out for the organic-inorganic hybrid complex of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) with an indium atom (In) to elucidate the degradation mechanism of thin films of molecular organic semiconductors by water molecules. This compound has been used as an organic semiconductor. The band gap of NTCDA was calculated to be as high as 3.39 eV as a single molecule, whereas a new band of NTCDA was formed as low-lying excited state (1.64 eV) after the interaction with the In atom. The water molecule attacked preferentially the In atom of In-NTCDA, and the solvation structure was formed around the In atom (solvation). Further addition of a water molecule to the system, the In atom is stripped off from NTCDA by water molecules, and solvation shell around the In atom is formed (separated solvation). The hydrogen-bond network was broken by the formation of solvation shell. The mechanism of degradation of the electron conductivity has been discussed on the basis of theoretical results. (c) 2007 Elsevier B.V All rights reserved.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 1 803 - 805 2008年01月 [査読有り][通常論文]
     
    The electronic states of potassium ion and atom (K(+) and K) adsorbed on the amorphous carbon surfaces have been investigated by means of hybrid density functional theory (DFT) calculation to elucidate the nature of interaction between K(+)/K and the amorphous carbon. Seven graphene sheets (n = 7, 14, 19, 29, 37, 44, and 52, where n means numbers of rings in each carbon cluster) were considered as models of amorphous carbon in the present study. The B3LYP/LANL2MB calculations showed that the potassium ion is located at ca. 2.80 angstrom from the graphene surfaces and the charge of K+ is not dependent on the cluster size of the graphene sheets. On the other hand, the charge of potassium atom (K) increased with increasing cluster size (n), and it reached a constant value (ca. +0.70) at n = 29-52. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [H. Tachikawa and A. Shimizu: J. Phys. Chem. B 110 (2006) 204451 was applied to diffusion processes of the K(+) ion and K atom on the model surfaces of amorphous carbon. The direct MO-MD calculations showed that the K(+) ion and K atom diffuse freely on the surface at 800K. The nature of the interaction between K(+)/K and the carbon clusters was discussed on the basis of theoretical results.
  • Nobuhito Kurono, Tadahiro Kondo, Masanori Wakabayashi, Hirohito Ooka, Tsutomu Inoue, Hiroto Tachikawa, Takeshi Ohkuma
    CHEMISTRY-AN ASIAN JOURNAL 3 8-9 1289 - 1297 2008年 [査読有り][通常論文]
     
    Enantiomer-selective carbamoylation of racemic alpha-hydroxy gamma-lactones with half equivalents of isocyanates in the presence of chiral Cu-II catalysts was studied. Among a series of catalyst bearing chiral bis(oxazoline) (box) and pyridine(bisoxazoline) ligands, [Cu(tBu-box)]X-2 [X=OSO2CF3 (3a), SbF6 (3b)] showed the highest enantioselectivity in the reaction of pantolactone (1a). Use of n-C3H7NCO, a small alkyl isocyanate, in CH2Cl2 solution was important to achieve a high level of enantiomer selection. The tBu-box-Cu-II catalyst efficiently differentiated two enantiomers of beta-substituted alpha-hydroxy gamma-lactones under the optimized reaction conditions, resulting in a stereoselectivity factor (s = k(fast)/k(slow)) of up to 209. Furthermore, this catalyst is highly active, so that the carbamoylation can be conducted with a substrate-to-catalyst molar ratio of 2000-3000. A catalytic cycle of this reaction is also proposed.
  • Shigeaki Abe, Takahiro Fukuzumi, Hiroto Tachikawa
    SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY 38 1 105 - 110 2008年 [査読有り][通常論文]
     
    Ab initio and density functional theory (DFT) calculations have been applied to hydration processes of dimethylsulfide (DMS), which plays an important role in cloud condensation nuclei (CCN) in marine boundary layer. The molecular complexes composed of water and dimethylsulfide, DMS(H(2)O)(n) (n = 0-3), were examined in the present calculations. The MP4SDQ/6311G(2d, p)//B3LYP/6-311G(d, p) calculations indicated that the binding energy of H(2)O to DMS is calculated to be 7.7 kcal/mol for n = 1. The second water molecule is bound to H(2)O of DMS(H(2)O) by a hydrogen bond, and then a 1: 2 complex is formed. The binding energy of the second water molecule to DMS(H(2)O) was calculated to be 10.4 kcal/mol. This energy is larger than that of water dimer (the corresponding binding energy was 6.6 kcal/mol in water dimer). Direct molecular orbital-molecular dynamics (MO-MD) calculations were carried out for the hydration reactions DMS(H(2)O) + H(2)O --> DMS(H(2)O)(2) (1) and H(2)O + H(2)O --> (H(2)O)(2) (2) at thermal collision energy. The calculations showed that water dimer formation reaction on DMS, reaction (1), is efficiently occurred, whereas half of the trajectories for reaction (2) gave dissociation products (H(2)O + H(2)O). The mechanism of hydration of DMS was discussed on the basis of theoretical results.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    SYNTHESIS AND REACTIVITY IN INORGANIC METAL-ORGANIC AND NANO-METAL CHEMISTRY 38 1 101 - 104 2008年 [査読有り][通常論文]
     
    Gas phase structures and electronic states of micro-solvated biomolecule clusters composed of water clusters and protonated Schiff Base Retinal (PSBR) have been investigated by means of hybrid density functional theory (DFT) method. Up to three-water molecules were considered as the water clusters, denoted by PSBR(H2O)(n) (n = 0-3). We focused our attention mainly on the effects of microsolvation on the infrared (IR) spectrum of PSBRs in the gas phase. The calculations showed that the water molecules bind strongly the N-H+ site of PSBR. The calculated IR spectra showed that the N-H stretching mode of PSBR is largely red-shifted by the interaction with water molecules. The similar calculations were carried out for methanol-PSBR clusters. The effects of microsolvation on the structure and electronic states were discussed on the basis of theoretical results.
  • Hiroshi Kawabata, Ken Tokunaga, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 1 420 - 424 2008年01月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation species of a fused thiophene oligomer, denoted by T(n), where n represents the number of thiophene rings in the oligomer, to elucidate the electronic structures at ground and low-lying excited states. A polymer of fused thiophene was also investigated using one-dimensional periodic boundary conditions (PBCs) for comparison. It was found that the reorganization energy of a radical cation of T(n) from a vertical hole trapping point to its relaxed structure is significantly small. Also, the reorganization energy decreased gradually with increasing n, indicating that T(n) has an effective hole transport property. It was found that the radical cation species of T(n) has a low energy band in the near-IR region, which is strongly correlated to hole conductivity. The relationship between the electronic states and hole conductivity was discussed on the basis of theoretical calculations.
  • Hiroshi Kawabata, Tetsuji Iyama, Hiroto Tachikawa
    JAPANESE JOURNAL OF APPLIED PHYSICS 47 1 800 - 802 2008年01月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for the lithium adsorbed on a fluorinated graphene surface (F-graphene, C(96)F(24)) to elucidate the effect of fluorination of amorphous carbon on the diffusion mechanism of lithium ion. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [H. Tachikawa and A. Shimizu: J. Phys. Chem. B 109 (2005) 13255] was applied to diffusion processes of the Li(+) ion on F-graphene. The B3LYP/LANL2MB calculation showed that the Li(+) ion is most stabilized around central position of F-graphene, and the energy was gradually instabilized for the edge region. The direct MO-MD calculations showed that the Li+ ion diffuses on the bulk surface region of F-graphite at 300 K. The nature of the interaction between Li+ and F-graphene was discussed on the basis of theoretical results.
  • Akira Miura, Shiro Shimada, Masaaki Yokoyama, Hiroto Tachikawa, Toshio Kitamura
    CHEMICAL PHYSICS LETTERS 451 4-6 222 - 225 2008年01月 [査読有り][通常論文]
     
    We investigated the properties of heavily oxygen-doped single GaN crystals and proposed their electronic structure based on first-principle calculations. The crystals were grown by carbothermal reduction and nitridation of Ga2O3 at 1180 degrees C for 2-8 h. The crystal were found to have high-crystallinity and high-concentration oxygen (4-9 x 10(20) atoms/cm(3)). Cathodoluminescence measurements of the 8-h-grown crystals showed a shift of band-edge-related luminescence peak toward higher energy (ca. 120 meV). Density of state of oxygen-doped GaN supercell was calculated using the first-principle to support this upward shift of luminescence energy. (C) 2007 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 10 16 2200 - 2206 2008年 [査読有り][通常論文]
     
    Dissociative electron capture dynamics of halocarbon absorbed on water cluster anion, caused by internal electron transfer from the water trimer anion to the halocarbon, have been investigated by means of the direct density functional theory (DFT)-molecular dynamics (MD) method. The CF2Cl2 molecule and a water trimer anion e(-)(H2O)(3) were used as a halocarbon and a trapped electron, respectively. First, the structure of trapped electron state, expressed by e(-)(H2O)(3)-CF2Cl2, was fully optimized. The excess electron was trapped by a dipole moment of water trimer. Next, initial geometries were randomly generated around the equilibrium point of the trapped electron state, and then trajectories were run. The direct DFT-MD calculations showed that the spin density distribution of excess electron is gradually changed from the water cluster (trapped electron state) to CF2Cl2 as a function of time. Immediately, the Cl- ion was dissociated from CF2Cl2- adsorbed on the water cluster. The reaction was schematically expressed bye(-)(H2O)(3)-CF2Cl2 ->[(H2O)(3)-CF2Cl2](-) -> (H2O)(3) + CF2Cl + Cl- (1)where [(H2O)(3)-CF2Cl2](-) indicates a transient intermediate state in which the excess electron is widely distributed on both the water cluster and CF2Cl2. The mechanism of the electron capture of halocarbon from the trapped electron in water ice was discussed on the basis of the theoretical results. Also, the dynamics feature was compared with those of the direct electron capture reactions of CF2Cl2 and CF2Cl2-(H2O)(3), i.e.e(-) + CF2Cl2, and e(-) + CF2Cl2-(H2O)(3), investigated in our previous paper [Tachikawa and Abe, J. Chem. Phys., 2007, 126, 194310].
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 692 25 5541 - 5548 2007年12月 [査読有り][通常論文]
     
    Structures and electronic states of paramagnetic species in co-deposit film composed of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) and aluminum (Al) have been investigated by means of hybrid density functional theory (DFT) calculations to determine the species in detail. Al-NTCDA 1:1 complex, 1:3 Al-3-NTCDA complex and an Al metal bridged dimer Al-(NTCDA)(2) were examined as paramagnetic species of Al-NTCDA complexes. The simulated electron paramagnetic resonance (EPR) spectra of the 1:3 complex and the dimer were in reasonable agreement with experiment reported previously by Tachikawa et al. [Tachikawa et al., J. Phys. Chem. B 109 (2005) 3139]. It was found that the contribution from the 1: 1 complex to the EPR spectra was very small. From the comparison with theoretical and experimental UV and EPR spectra, it was found that several paramagnetic and diamagnetic species exist in the co-deposit film of Al/NTCDA. The structures and electronic states were discussed on the basis of theoretical results. (C) 2007 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 111 40 10134 - 10138 2007年10月 [査読有り][通常論文]
     
    The mechanism of excess electron and hole localizations in radical ions of poly(dimethylsilane) (PDMS) has been investigated by means of molecular dynamics (MD) and extended Huckel methods. Oligo(dimethylsilane) composed of 100 monomer units of dimethylsilane, CH3(Si(CH3)(2))(n)CH3 (n = 100), were used as a model of PDMS. Both wings of the oligomer were capped by a methyl group. First, the geometry of PDMS with a regular all-trans form was fully optimized by MM2(+) energy gradient method. Next, the MD calculation was carried out for PDMS at 300 K. The structure of PDMS was gradually deformed as a function of simulation time, especially the dihedral angle of Si-Si-Si-Si backbone that was randomized. At time zero when the structure has the regular all-trans form, both the excess electron and hole were completely delocalized on the Si backbone of PDMS. After thermal activation, the localization of the electron and hole was found. The mechanism of the localization was discussed on the basis of theoretical results.
  • Shinichi Enami, Takashi Yamanaka, Satoshi Hashimoto, Masahiro Kawasaki, Kenichi Tonokura, Hiroto Tachikawa
    CHEMICAL PHYSICS LETTERS 445 4-6 152 - 156 2007年09月 [査読有り][通常論文]
     
    Formation of the iodine monoxide radical (IO) was observed during the reaction of iodoalkyl radicals (RCHI) or cyclo-C6H10I radical with O-2 at 298 K using cavity ring-down spectroscopy, where R stands for CnH2n+l (n = 0-3). The yields of IO from the reactions of various RCH2I species with Cl atom in the presence of O-2 were determined. The energy level diagrams derived from theoretical calculations for each individual reaction support the formation of IO radicals via a direct RCHI radical oxidation pathway. (C) 2007 Elsevier B.V. All rights reserved.
  • Kei Iokibe, Kazuhisa Azumi, Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 111 36 13510 - 13516 2007年09月 [査読有り][通常論文]
     
    The adsorption and diffusion of a Zn atom on a Zn(001) surface has been investigated theoretically by using first-principles periodic boundary condition calculations to elucidate the mechanism of crystal growth of zinc in a Zn surface. Three surface models, terrace, step, and kink, of the Zn(001) surface were considered as adsorption sites in the present study. The most stable site in the terrace model was the on-top site, where the zinc adatom is bound to only one zinc atom of the surface. The activation barrier between the on-top site and the next on-top site was negligibly low (the activation energy is 44 meV at the PW91/LANL2DZ level), suggesting that the Zn adatom diffuses easily on the Zn(001) surface. The Zn adatom was more stabilized at the step site (752 meV) and kink site (935 meV) with respect to the on-top site. It was found that the magnitude of 4s-4p orbital mixing of the Zn adatom (hybridization) is strongly related to the binding energy. The mechanism of the adsorption of Zn on Zn(001) surfaces was discussed on the basis of theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY C 111 35 13087 - 13091 2007年09月 [査読有り][通常論文]
     
    The diffusion dynamics of the Li+ ion on fullerene (C-60) have been investigated by means of the direct molecula-orbital-molecular dynamics (MO-MD) method. The total energy and energy gradient on the full dimensional potential energy surface of the Li(+)C60 system were calculated at each time step in the trajectory calculation. The optimized structure, where the Li+ ion is located at the hexagonal Site Of C60, was used as an initial itructure at time zero. Simulation temperatures were chosen in the range of 10-300 K. The dynamics calculations showed that the Li+ ion vibrates around the initial equilibrium point below 40 K, while the ion can move above 50 K. At low temperature (below 300 K), the diffusion coefficients for the Li+ ion on the C60 surface are larger than those of the graphite surface. The diffusion coefficients on both C60 and the graphite surface were almost equivalent at medium temperatures around 300 K. At higher temperatures (T > 300 K), the coefficients for the graphite surface were significantly larger than those Of C60. On the basis of theoretical results, A e designed an ion-switching molecular device composed Of C60 and graphite sheet.
  • Hong-Yan Xiao, Jun Cao, Ya-Jun Liu, Wei-Hai Fang, Hiroto Tachikawa, Masaru Shiotani
    JOURNAL OF PHYSICAL CHEMISTRY A 111 24 5192 - 5200 2007年06月 [査読有り][通常論文]
     
    The s-cis and s-trans isomer radical cations of hexafluoro-1,3-butadiene (s-cis-HFBD+ and s-trans-HFBD+) were generated by a gamma-irradiated solid solution of the neutral HFBD molecule in solid matrix at 77 K and observed by means of electron spin resonance (ESR) and electronic spectroscopies. In comparing the experimental isotropic and anisotropic F-19 hyperfine splittings with the computational ones by the DFT B3LYP and MP2 methods, the generated s-cis-HFBD+ and s-trans-HFBD+ radical cations were confirmed to be (2)A(2) and B-2(g) electronic ground states in C-2v and C-2h symmetries, respectively. The present spectroscopic study revealed that the relative abundance of s-cis-HFBD+ to s-trans-HFBD+ was 4.0 immediately after being formed by gamma-irradiation, and subsequently most s-cis-HFBD+ was isomerized to s-trans-HFBD+ by visible-light illumination with 500-600 nm wavelength. The process of nonplanar HFBD ionizing to form stable planar s-cis- and s-trans-HFBD+ and the reaction mechanism of the cis-to-trans photoisomerization were discussed by (MS-)CASPT2//CASSCF calculated vertical excitation energies (T-v) and torsional potential energy curves (TPECs) of HFBD and HFBD+.
  • Hiroto Tachikawa, Shigeaki Abe
    JOURNAL OF CHEMICAL PHYSICS 126 19 2007年05月 [査読有り][通常論文]
     
    The electron capture dynamics of halocarbon and its water complex have been investigated by means of the full dimensional direct density functional theory molecular dynamics method in order to shed light on the mechanism of electron capture of a halocarbon adsorbed on the ice surface. The CF2Cl2 molecule and a cyclic water trimer (H2O)(3) were used as halocarbon and water cluster, respectively. The dynamics calculation of CF2Cl2 showed that both C-Cl bonds are largely elongated after the electron capture, while one of the Cl atoms is dissociated from CF2Cl2- as a Cl- ion. Almost all total available energy was transferred into the internal modes of the parent CF2Cl radical on the product state, while the relative translational energy of Cl- was significantly low due to the elongation of two C-Cl bonds. In the case of a halocarbon-water cluster system, the geometry optimization of neutral complex CF2Cl2(H2O)(3) showed that one of the Cl atoms interacts with n orbital of water molecules of trimer and the other Cl atom existed as a dangling Cl atom. After the electron capture, only one C-Cl bond (dangling Cl atom) was rapidly elongated, whereas the other C-Cl bond is silent during the reaction. The dangling Cl atom was directly dissociated from CF2Cl2-(H2O)(3) as Cl-. The fast Cl- ion was generated from CF2Cl2-(H2O)(3) on the water cluster. The mechanism of the electron capture of halocarbon on water ice was discussed on the basis of the theoretical results. (C) 2007 American Institute of Physics.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 692 7 1511 - 1518 2007年03月 [査読有り][通常論文]
     
    The electronic states of radical cations of oligo[methyl(phenyl)silane] (OMPSi+) with all trans form (n = 2-8, where n is number of monomer unit of OMPSi) have been investigated by means of density functional theory (DFT) calculation to shed light on the mechanism of hole-transport in oligosilanes with phenyl group in the side chain. For the shorter oligomers (n < 3), the hole (unpaired electron) was widely distributed equivalently in both the Si main and side chains (55% for the Si main chain and 45% for the side chain). The distribution of hole on the chains was largely changed as a function of chain lengths (n). Ratios of the hole distribution on the main and side chains became almost constant at n = 7-8: 70% of spin density was distributed on the Si-main chain and 30% on the side-chain, which is much different from that of oligo(dimethyl)silane (the spin density on the methyl side chain was less than 3% of spin density). From these results, it was concluded that the hole in OMPSi+ can transfer by the mechanism for both intermolecular and the intrachain hole-transfer processes. (c) 2006 Elsevier B.V. All rights reserved.
  • Hiroshi Kawabata, Kazumi Matsushige, Shigekazu Ohmori, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 472 687 - 695 2007年 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral and radical cation of permethyl-oligogermane, Ge-n(CH3)(2n+2) (n=4-28), to elucidate the electronic structures at ground and low-lying excited states. It was found that a hole is distributed in both the Ge-Ge skeleton (main chain) and methyl group (side chain) in the case of shorter chain-lengths below n = 8, whereas the spin density (hole) in the methyl group becomes significantly smaller in longer chain-lengths (n > 10). The IR-band of radical cation were assigned on the basis of theoretical calculations.
  • Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 472 697 - 704 2007年 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for the lithium ion-carbon cluster model systems to elucidate the nature of lithium-carbon surface interaction. Also, direct molecular orbital-molecular dynamics (MO-MD) calculation [Tachikawa and Shimizu, J. Phys. Chem. B, 109 (2005) 13255] was applied to diffusion processes of the Li ion on the model surfaces of amorphous carbon. Seven cluster models (n = 7, 14, 19, 29, 37, 44 and 55, where n means numbers of rings in the carbon cluster models) were considered in the present study. The B3LYP/LANL2MB calculations showed that the lithium ion is located at ca. 1.60 angstrom from the carbon surface. The direct MO-MD calculations showed that the Li ion diffuses freely on the surface above 250 K. At higher temperature (1100 K), the Li ion moves from the center to edge region of the model surface and leaves from the surface. The nature of the interaction between Li+ and the carbon clusters was discussed on the basis of theoretical results.
  • Kei Iokibe, Hiroto Tachikawa, Kazuhisa Azumi
    JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 40 2 427 - 436 2007年01月 [査読有り][通常論文]
     
    Ab-initio and density functional theory (DFT) calculations have been carried out for zinc clusters Zn-n (n = 2-32, n is the number of atoms to form a cluster) to elucidate the structure and electronic charge states of the clusters and the mechanism of clustering. The binding energies of Zn atoms were negligibly small at n = 2-3, whereas the energy increased significantly at n = 4 (the first transition). The second transition occurred at n = 8-16. In the larger clusters (n = 16-32), the binding energy increased slightly with increasing cluster size (n). The cluster size dependence of the binding energy and bond length between zinc atoms agreed well with that of the natural population of electrons in the 4p orbital of the zinc atom. In the larger clusters (n > 20), it was found that the zinc atoms in the surface region of the cluster have a positive charge, whereas those in the interior region have a negative charge with a large population in the 4p orbital. The formation mechanism of zinc clusters was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF CHEMICAL THEORY AND COMPUTATION 3 1 184 - 193 2007年01月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for the radical cation and anion of permethyloligosilane Si-n(CH3)(2n+2)(+/-) (n = 2-6) to elucidate the electronic structures at ground and low-lying excited states, and the results were compared with the corresponding experimental values. In particular, the assignment of electronic transition appeared at near-IR and visible regions, which is strongly correlated to hole and electron conductivity, and was carried out on the basis of time-dependent DFT calculation. The structure of oligosilane was generated at 300 K by direct PM3 molecular dynamics calculations, and then the geometry was fully optimized at the DFT(B3LYP)/6-311+G(d,p) level. It was found that the hole in the radical cation and the electron in the radical anion of oligosilane are delocalized over the Si skeleton. The proton-hyperfine coupling constants calculated were in good agreement with those obtained by an electron spin resonance experiment. It was also found that the g-anisotropy of the radical anion was significantly larger than that of the radical cation. The IR bands of radical ions were assigned on the basis of theoretical calculations.
  • Hiroto Tachikawa, Kei Iokibe, Kazuhisa Azumi, Hiroshi Kawabata
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS 9 30 3978 - 3984 2007年 [査読有り][通常論文]
     
    Ab initio and Density Functional Theory (DFT) calculations have been carried out for zinc-water clusters Zn-n-(H2O)m (n = 1-32 and m = 1-3, where n and m are the numbers of zinc atoms and water molecules, respectively) to elucidate the structure and electronic states of the clusters and the interaction of zinc cluster with water molecules. The binding energies of H2O to zinc clusters were small at n = 2-3 (2.3-4.2 kcal mol(-1)), whereas the energy increased significantly in n = 4 (9.0 kcal mol(-1)). Also, the binding nature of H2O was changed at n = 4. The cluster size dependency of the binding energy of H2O accorded well with that of the natural population of electrons in the 4p orbital of the zinc atom. In the larger clusters (n > 20), it was found that the zinc atoms in surface regions of the zinc cluster have a positive charge, whereas those in the interior region have a negative charge with the large electron population in the 4p orbital. The interaction of H2O with the zinc clusters were discussed on the basis of the theoretical results.
  • Hiroshi Kawabata, Shigekazu Ohmori, Kazumi Matsushige, Hiroto Tachikawa
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 691 26 5525 - 5530 2006年12月 [査読有り][通常論文]
     
    Hybrid density functional theory (DFT) calculations have been carried out for neutral, radical cation and dication of permethyloligosilane, Si-n(CH3)(2n+2) (n=4-30), to elucidate the electronic structures at ground and low-lying excited states. It was found that a hole is distributed in both the Si-Si skeleton (main chain) and methyl group (side chain) in the case of shorter chain-lengths below n=6, whereas the spin density (hole) in the methyl group becomes significantly smaller in longer chain-lengths (n > 7). The IR-band of radical cation were assigned on the basis of theoretical calculations. (c) 2006 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Shigeaki Abe
    CHEMICAL PHYSICS LETTERS 432 4-6 409 - 413 2006年12月 [査読有り][通常論文]
     
    The excitation energies of O-3-H2O complex have been calculated by means of SAC-Cl method to elucidate the spectral shifts of excitation energies of O-3 caused by the complex formation with a water molecule. The eclipsed form, where the center oxygen of O-3 and water oxygen are located on the C, molecular plane, was examined in the present study. The first and third excitation energies of O-3 were slightly blue-shifted by the complex formation with H2O. The oscillator strength for the third excitation was not affected by the complex formation, indicating that the photo-dissociation of the O-3-H2O Complex occurs efficiently as well as free ozone molecule. The electronic states of the complex was discussed on the basis of theoretical results. (c) 2006 Elsevier B.V. All rights reserved.
  • Hiroto Tachikawa, Hiroshi Kawabata
    JOURNAL OF ORGANOMETALLIC CHEMISTRY 691 23 4843 - 4849 2006年11月 [査読有り][通常論文]
     
    The electronic structures at the ground and low-lying excited states of permethyloligosilane radical cations, Si-n(CH3)(2n+2)(+) (n = 4-7), have been investigated using DFT and ab initio calculations. The calculations showed that positive charge (hole) is delocalized along the Si-Si main chain at the ground and first excited states. On the other hand, the hole is transferred to the methyl side-chain at the second and higher excited states. From these results, it was concluded that hole can move along the Si-Si main chain at thermal conditions. Also, it was predicted that intermolecular hole hopping takes place by photo-irradiation to the permethyloligosilane radical cation. The mechanism of hole transfer was discussed on the basis of the results. (c) 2006 Elsevier B.V. All rights reserved.
  • KONDO Satomi, HASHIMOTO Kenro, TACHIKAWA Hiroto
    Chem. Phys. Lett. 431 1-3 45 - 50 2006年11月 [査読有り][通常論文]
     
    The dynamics of Na(H2O) following electron detachment from Na-(H2O) in a zero-point vibrational state was investigated using an ab initio direct molecular-dynamics method. In 96% of the trajectories of Na(H2O), the reorientations of water occurred on the similar to 120 fs time scale. Na-O bond formation was observed in more than 80% of the neutral trajectories. The photodetachment-photoionization spectra using 4.3-5.3 eV photons delayed from electron detachment were calculated for 5 ps. (c) 2006 Elsevier B.V. All rights reserved.
  • Takahiro Itoh, Toshiaki Mase, Takashi Nishikata, Tetsuji Iyama, Hiroto Tachikawa, Yuri Kobayashi, Yasunori Yarnamoto, Norio Miyaura
    TETRAHEDRON 62 41 9610 - 9621 2006年10月 [査読有り][通常論文]
     
    An enantioselective synthesis of acyclic beta-diaryl ketones and esters via 1,4-addition of arylboronic acids to beta-aryl-alpha,beta-unsaturated ketones or esters is described. The complex in situ prepared from [Rh(nbd)(2)]BF4 and chiraphos was found to be an excellent catalyst to achieve high enantioselectivities in a range of 83-89% ee for the ketone derivatives and 78-94% ee for tert-butyl beta-arylacrylate derivatives. The protocol provided a catalytic method for the enantioselective synthesis of selective endothelin A receptor antagonists (7, 8) reported by SmithKline Beecham and Merck-Banyu. The enantioselection mechanism and efficiency of the chiraphos ligand for beta-aryl-alpha,beta-unsaturated ketones and esters are discussed on the basis of results of DFT computational studies on the modes of coordination of the enone substrates to the phenylrhodium(I)-(S,S)-chiraphos complex. (c) 2006 Elsevier Ltd. All rights reserved.
  • Shinichi Enami, Takashi Yamanaka, Satoshi Hashimoto, Masahiro Kawasaki, Simone Aloisio, Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 125 13 133116 - 133122 2006年10月 [査読有り][通常論文]
     
    The broad absorption of Cl-3 radical was observed between 1150 and 1350 nm using cavity ring-down spectroscopy at 213-265 K and 50-200 Torr with He, N-2, Ar, or SF6 diluents. The absorption intensity of Cl-3 increased at lower temperature and higher pressure. SF6 was the most efficient diluent gas. The temperature dependent equilibrium constants for Cl-3 formation from Cl+Cl-2 were theoretically calculated at the MP4SDQ/6-311+G(d) level. Observed decay time profiles of Cl-3 and the pressure dependence of Cl-3 formation are explained by the equilibrium reaction and a decay reaction of Cl+Cl-3. (c) 2006 American Institute of Physics.
  • Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 125 13 133119 - 133129 2006年10月 [査読有り][通常論文]
     
    Reaction dynamics for a microsolvated S(N)2 reaction OH-(H2O)+CH3Cl have been investigated by means of the direct ab initio molecular dynamics method. The relative center-of-mass collision energies were chosen as 10, 15, and 25 kcal/mol. Three reaction channels were found as products. These are (1) a channel leading to complete dissociation (the products are CH3OH+Cl-+H2O: denoted by channel I), (2) a solvation channel (the products are Cl-(H2O)+CH3OH: channel II), and (3) a complex formation channel (the products are CH3OH center dot center dot center dot H2O+Cl-: channel III). The branching ratios for the three channels were drastically changed as a function of center-of-mass collision energy. The ratio of complete dissociation channel (channel I) increased with increasing collision energy, whereas that of channel III decreased. The solvation channel (channel II) was minor at all collision energies. The selectivity of the reaction channels and the mechanism are discussed on the basis of the theoretical results. (c) 2006 American Institute of Physics.
  • Hiroto Tachikawa, Akira Shimizu
    JOURNAL OF PHYSICAL CHEMISTRY B 110 41 20445 - 20450 2006年10月 [査読有り][通常論文]
     
    Direct molecular orbital-molecular dynamics (MO-MD) calculation was applied to diffusion processes of the Li atom on a model surface of amorphous carbon and compared with the diffusion mechanism of Li+ ion. A carbon sheet composed of C96H24 was used as the model surface. The total energy and energy gradient on the full dimensional potential energy surface of the LiC96H24 system were calculated at each time step in the trajectory calculation. The optimized structure, where the Li atom is located at the center of mass of the model surface, was used as the initial structure at time zero. Simulation temperatures were chosen in the range of 200-1250 K. The dynamics calculations showed that the Li atom vibrates around the initial position below 250 K, and it moves above 300 K. At middle temperature, the Li atom translates freely on the surface. At higher temperature (1000 K), the Li atom moves from the center to edge region of the model surface and is trapped in the edge. The activation energy calculated for the Li atom is larger than that for the Li+ ion. This difference is due to the fact that the Li atom diffuses together with an unpaired electron on the carbon surface. The diffusion mechanism of the Li atom was discussed on the basis of the theoretical results.
  • Hiroto Tachikawa
    JOURNAL OF CHEMICAL PHYSICS 125 14 144307 - 144315 2006年10月 [査読有り][通常論文]
     
    Electron attachment dynamics of excess electron in water cluster (H2O)(n) (n=2 and 3) have been investigated by means of full-dimensional direct ab initio molecular dynamics (MD) method at the MP2/6-311++G(d,p) level. It was found that the hydrogen bond breaking due to the excess electron is an important process in the first stage of electron capture in water trimer. Time scale of electron localization and hydrogen bond breaking were determined by the direct ab initio MD simulation. The initial process of hydration in water cluster is clearly visualized in the present study. In n=3, an excess electron is first trapped around the cyclic water trimer with a triangular form, where the excess electron is equivalently distributed on the three water molecules at time zero. After 50 fs, the excess electron is concentrated into two water molecules, while the potential energy of the system decreases by -1.5 kcal/mol from the vertical point. After 100 fs, the excess electron is localized in one of the water molecules and the potential energy decreases by -5.3 kcal/mol, but the triangular form still remained. After that, one of the hydrogen bonds in the triangular form is gradually broken by the excess electron, while the structure becomes linear at 100-300 fs after electron capture. The time scale of hydrogen bond breaking due to the excess electron is calculated to be about 300 fs. Finally, a dipole bound state is formed by the linear form of three water molecules. In the case of n=2, the dipole bound anion is formed directly. The mechanism of electron hydration dynamics was discussed on the basis of theoretical results. (c) 2006 American Institute of Physics.
  • Hiroto Tachikawa, Manabu Igarashi
    CHEMICAL PHYSICS 324 2-3 639 - 646 2006年05月 [査読有り][通常論文]
     
    Direct ab initio molecular dynamics (MD) calculations have been applied to a S(N)2 reaction OH- + CH3Cl -> CH3OH + Cl-. The collision dynamics with non-zero impact parameters were treated in the present study, and the results are compared with the near collinear collision dynamics previously reported by us [H. Tachikawa, M. Igarashi, T. Ishibashi, J. Phys. Chem. A 106 (2002) 10977]. The collision energy was fixed to 25 kcal/mol. The product state distribution obtained for the non-zero impact parameter collision dynamics was slightly different from that of the collinear collision. The distribution of relative translational energy between products Cl- and CH3OH in the non-zero impact parameter collision dynamics was shifted to higher energy region from that of collinear collision. Also, it was found that the mean translational energy of the product has a maximum at non-zero impact parameter (b = 0.6-1.2 angstrom). The reaction mechanism is discussed on the basis of theoretical results. (c) 2005 Elsevier B.V. All rights reserved.
  • H Tachikawa
    JOURNAL OF PHYSICAL CHEMISTRY A 110 1 153 - 159 2006年01月 [査読無し][通常論文]
     
    Ionization processes of chlorobenzene-ammonia 1:1 complex (PhCl-NH3) have been investigated by means of full dimensional direct ab initio molecular dynamics (MD) method, static ab initio calculations, and density functional theory (DFT) calculations. The static ab initio and DFT calculations of neutral PhCl-NH3 complex showed that one of the hydrogen atoms of NH3 orients toward a carbon atom in the para-position of PhCl. The dynamics calculation for ionization of PhCl-NH3 indicated that two reaction channels are competitive with each other as product channels: one is an intramolecular S(N)2 reaction expressed by a reaction scheme [PhCl-NH3](+) -> S(N)2 intermediate complex -> PhNH3+ + Cl, and the other is ortho-NH3 addition complex (ortho complex) in which NH3 attacks the ortho-carbon of PhCl+ and the trajectory leads to a bound complex expressed by (PhCl-NHS3)(+). The mechanism of the ionization of PhCl-NH3 is discussed on the basis of the theoretical results.
  • T. Kumada, H. Tachikawa, and T. Takayanagi: "H6+ in irradiated solid para-hydrogen and its decay dynamics: Reinvestigation of quartet electron paramagnetic resonance lines assigned to H2-" Phys. Chem. Chem. Phys., 7, 776-784 (2005)*
    2005年 [査読無し][通常論文]
  • H. Tachikawa, M. Igarashi, J. Nishihira, and T. Ishibashi: "Ab initio model study on acetylcholinesterase catalysis: Potential Energy Surfaces of the Proton Transfer Reactions" J. Photochem. Photobiol. B:Biol. 79, 11-23 (2005)*
    2005年 [査読無し][通常論文]
  • H. Tachikawa, H. Kawabata, K. Ishida and K. Matsushige: "A DFT and direct MO dynamics Study on the structures and electronic states of phenyl-capped terthiophene" J. Organometal. Chem., 690, 2895-2904 (2005)*
    2005年 [査読無し][通常論文]
  • T. Takada and H. Tachikawa: "Hybrid DFT Study of the Hyperfine Coupling Constants of Methyl Radicals in Model Matrix Lattices" Int. J. Quant. Chem., 105, 79-83 (2005)*
    2005年 [査読無し][通常論文]
  • H. Tachikawa, T. Iyama, and H. Kawabata: "Potential energy curves along the diffusion paths of NO on the small-sized Cu(100) model cluster" J. Mol. Struct. (THEOCHEM), 718, 117-122 (2005)*
    2005年 [査読無し][通常論文]
  • H. Tachikawa and A. Shimizu: "Diffusion Dynamics of the Li+ Ion on a Model Surface of Amorphous Carbon: A Direct Molecular Orbital Dynamics Study" J. Phys. Chem. B, 109, 13255-13262 (2005)*
    2005年 [査読無し][通常論文]
  • H. Tachikawa: "SN2 and SN2′ reaction dynamics of cyclopropenyl chloride with halide ion : A direct ab initio molecular dynamics (MD) study" Can. J. Chem. 83, 1597-1605 (2005)*
    2005年 [査読無し][通常論文]
  • Yabushita, A., Hashikawa, Y., Ikeda, A., Kawasaki, M., Tachikawa, H.: “Hydrogen atom formation from the Photodissociation of water ice at 193 nm” J. Chem. Phys. 120, 5463-5468 (2004)*
    2004年 [査読無し][通常論文]
  • Iyama, T., Tachikawa, H.: “Trans-Cis Isomerization of Protonated Schiff Base of Retinal at the Ground and Triplet States: A Hybrid DFT Study” Int. Elec. J. Molec. Design, 3, 37-44 (2004)*
    2004年 [査読無し][通常論文]
  • Iyama, T., Tachikawa, H.: “Potential energy curves for the isomerization of protonated Schiff base of retinal on the triplet state surface” Mol. Simul. 30, 917-921 (2004)*
    2004年 [査読無し][通常論文]
  • Kawasaki, M., Sugita, A., Ramos, C., Matsumi Y., Tachikawa, H.: “Photodissociation of water dimer at 205 nm” J. Phys. Chem. A., 108, 8119-8124 (2004)*
    2004年 [査読無し][通常論文]
  • Tachikawa, H.: “Ionization dynamics of the small-sized water clusters: A direct ab initio trajectory study” J. Phys. Chem. A. 108, 7853-7862 (2004)*
    2004年 [査読無し][通常論文]
  • Tachikawa, H, Iyama, T.: “TD-DFT calculations of the Potential Energy Curves for the Trans-Cis Photo- isomerization of Protonated Schiff base of Retinal” J. Photochem. Photobiol. B:Biol. 76, 55-60 (2004)*
    2004年 [査読無し][通常論文]
  • H Tachikawa, S Abe
    INORGANIC CHEMISTRY 42 7 2188 - 2190 2003年04月 [査読無し][通常論文]
     
    Ab initio MO calculations have been carried out for the ozone-water 1:1 complexes in order to elucidate the structures and electronic state of the complexes. The QCISD calculations indicated that three structures are obtained as stable forms Of O-3-H2O. The most stable structure Of O-3-H2O has C, symmetry where the central oxygen Of O-3 and all atoms of H2O are located on the molecular C, plane. The dipole of H2O orients toward the central oxygen atom Of O-3 (i.e., dipole orientation form). The other two forms are cis and trans forms Of O-3-H2O where all atoms are located on the molecular plane, and a hydrogen of H2O binds to one of the terminal oxygen atoms Of O-3 by a hydrogen bond. The binding energies Of O-3 to H2O for dipole, cis, and trans forms are calculated to be 2.39, 2.27, and 2.30 kcal/mol, respectively, at the QCISD(T)/6-311++G(3df,3pd)//QCISD/6-311++G((d,p) level. The dipole orientation form is more stable in energy than the cis and trans forms. Rotational constants for the dipole orientation form are calculated to be A = 11.897, B = 4.177, and C = 3.318 GHz which are in good agreement with the experimental values (A = 11.961, B = 4.174, and C = 3.265 GHz). The electronic states Of O-3-H2O were discussed on the basis of theoretical results.
  • Kawabata, H., Tachikawa, H.: "Ab initio and hybrid DFTstudy on the electronic states of fluorenone-Na complexes" Phys. Chem. Chem. Phys., 5, 3587-3590 (2003)*
    2003年 [査読無し][通常論文]
  • Tachikawa, H., Abe, S.: "Ozone-Water 1:1 Complexes O3-H2O: An Ab Initio Study" Inorg. Chem., 42, 2188-2190 (2003)*
    2003年 [査読無し][通常論文]
  • Tachikawa, H., Iyama, T., Fukuzumi, T.: "Decomposition dynamics of interstellar HCNH: Ab-initio MO and RRKM studies" Astronomy & Astrophysics, 397, 1-6 (2003)*
    2003年 [査読無し][通常論文]
  • Tachikawa, H., Kawabata, H. : "Ab-initio DFT study on the mechanism of the electron conductivity of molecular devices composed of indium atoms and C=O carbonyl compounds" J. Mater. Chem., 13, 1293-1297 (2003)*
    2003年 [査読無し][通常論文]
  • Tachikawa, H., Kawabata, H. : "Dynamics of the Hole-Capture Processes in Biphenyl and Poly(4-vinylbiphenyl): A Direct ab Initio Trajectory Study" J. Phys. Chem. B., 107, 1113-1119 (2003)*
    2003年 [査読無し][通常論文]
  • Seki, T., Tachikawa, H., Yamada, T., Hattori, H.: "Synthesis of phthalide-skelton using selective intramolecular Tishchenko reaction over solid base catalysts" J. Catalysis, 217, 117-126 (2003)*
    2003年 [査読無し][通常論文]
  • Igarashi, M., Ishibashi, T., Nishihira, J., Tachikawa, H.: "Energetics of Catalytic Reaction of Acetylcholinesterase (AChE) with Acetylcholine (ACh): Role of the Oxyanion Hole" Int. Elec. J. Mol. Design, 2, 712-722 (2003)*
    2003年 [査読無し][通常論文]
  • Tachikawa, H., Kawabata, H.: "Structures and electronic states of gallium-acetone complexes: ab-initio DFT study" J. Organometal. Chem., 678, 56-60 (2003)*
    2003年 [査読無し][通常論文]
  • Tachikawa, H., Igarashi, M., Ishibashi, T.: "Ionization Dynamics of trans-Formanilide-H2O Complexes: A Direct ab Initio Dynamics Study" J. Phys. Chem. A., 107, 7505-7513 (2003)*
    2003年 [査読無し][通常論文]
  • Tachikawa, H.: " Electron capture dynamics of the water dimer: a direct ab initio dynamics study", Chem. Phys. Lett., 370, 188-196 (2003)*
    2003年 [査読無し][通常論文]
  • Konno, H., Shiba, K., Tachikawa, H., Nakahashi, T., Oka, H., and Inagaki, M.” Nanospace due to the presence of boron and nitrogen in carbon films prepared from polyimide”, Symthetic Metal., 125:189-196 (2002)*
    2002年 [査読無し][通常論文]
  • Shimizu, A., and Tachikawa, H.:” The direct molecular orbital dynamics study on the hydrogen species adsorbed on the surface of planar graphite cluster model”, J. Phys. Chem. Solid, 63:759-763 (2002)*
    2002年 [査読無し][通常論文]
  • Tachikawa, H., Igarashi, M., and Ishibashi, T.: “A direct ab initio trajectory study on a microsolvated SN2 reaction, F-(H2O) + CH3Cl at hyperthermal collision energy”, Chem. Phys. Lett., 363: 355-361 (2002)*
    2002年 [査読無し][通常論文]
  • Tachikawa, H.:”A full dimensional ab-initio direct trajectory study on the ionization dynamics of SiH4”, Phys. Chem. Chem. Phys., 4:1135-1140 (2002)*
    2002年 [査読無し][通常論文]
  • Tachikawa, H.:”Ab-initio MO calculations of structures and Electronic States of SF and SF6-“, J. Phys. B., 35:55-60 (2002)*
    2002年 [査読無し][通常論文]
  • Shimizu, A., and Tachikawa, H.:”Diffusion of Li+ ion in graphite cluster model at 800 K: a direct molecular orbital dynamics study”, J. Phys. Chem. Solid, 63:619-624 (2002)*
    2002年 [査読無し][通常論文]
  • Igarashi, M., Ishibashi, T, and Tachikawa, H.:”A direct ab initio molecular dynamics study of the finite temperature effects on the hyperfine coupling constant of methyl radical-water complexes”, J. Mol. Struct. (THEOCHEM), 594:61-69 (2002)*
    2002年 [査読無し][通常論文]
  • Tachikawa, H., Igarashi, M., and Ishibashi, T.:”Ab initio molecular dynamics (MD) calculations of hyperfine coupling constants of methyl radical”, Chem. Phys. Lett., 352:113-119 (2002)*
    2002年 [査読無し][通常論文]
  • Tachikawa, H., and Iyama, T.:”Electron Detachment Dynamics of the Microsolvated Benzophenone radical anion-A full dimensional direct Ab-initio Trajectory Approach”, Phys. Chem. Chem. Phys., 4:5806-5812 (2002)*
    2002年 [査読無し][通常論文]
  • Tachikawa, H.:”An ab-initio direct trajectory study on the ionization processes of the Benzene-NH3 complexes - Electronic state dependence on the complex formation processes”, Phys. Chem. Chem. Phys., 4:6018-6026 (2002)*
    2002年 [査読無し][通常論文]
  • Tachikawa, H.;”A Direct ab-Initio Trajectory Study on the Ionization Dynamics of the Water Dimer”, J. Phys. Chem. A., 106: 6915-6921 (2002)*
    2002年 [査読無し][通常論文]
  • T. Seki, H. Kabashima, K. Akutsu, H. Tachikawa, and H. Hattori:"Mixed Tishchenko Reaction over Solid Base Catalysts", J. Catal., 204, 393-401 (2001)*
    2001年 [査読無し][通常論文]
  • H. Tachikawa and T. Yamano:"Ab-initio MO calculations of hyperfine coupling constants of hydronium radical H3O", Chem. Phys. Lett., 335, 305-310 (2001)*
    2001年 [査読無し][通常論文]
  • H. Tachikawa and T. Yamano:"A full dimensional direct ab-initio dynamics study of the electron capture by SF6",Chem. Phys., 264, 81-89 (2001)*
    2001年 [査読無し][通常論文]
  • A. Shimizu and H. Tachikawa:"Dynamics of hydrogen and proton trapped in diamond lattice: A Direct MO dynamics approach", J. Chem. Eng. Jpn., 34, 207-210 (2001)*
    2001年 [査読無し][通常論文]
  • H. Konno, K. Shiba, H. Tachikawa, T. Nakahashi, H. Oka, and M. Inagaki:"Nanospace due to the presence of boron and nitrogen in carbon films prepared from polyimide", Symthetic Metal, 125, 189-196 (2001)*
    2001年 [査読無し][通常論文]
  • A. Shimizu and H. Tachikawa:"Thermal vibrations of Li+ ion and Li atom at the circumference of graphite cluster model:A Direct molecular dynamics calculation", J. Mol. Struct. (THEOCHEM), 544, 173-180 (2001)*
    2001年 [査読無し][通常論文]
  • H. Tachikawa:"Ionization dynamics of CF4-H2O complexes: A Full Dimensional ab-initio trajectory Study", Chem. Phys., 273, 149-157 (2001)*
    2001年 [査読無し][通常論文]
  • H. Tachikawa, M. Igarashi and T. Ishibashi:"Vibrational frequency-shifts of H2O caused by complex formation with a molecular cation: A density Functional Study", Phys. Chem. Chem. Phys., 3, 3052-3056 (2001)*
    2001年 [査読無し][通常論文]
  • A. Shimizu and H. Tachikawa:"The dynamics on migrations of Li+ ion and Li atom at 700 K around the circumference of graphite cluster model: A direct molecular dynamics Study", Chem. Phys. Lett. 339, 110-116 (2001)*
    2001年 [査読無し][通常論文]
  • Y Aoki, H Konno, H Tachikawa, M Inagaki
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 73 5 1197 - 1203 2000年05月 [査読有り][通常論文]
     
    Single phase LnCrO(4) (Ln = La-Nd) compounds were attempted to synthesize by the pyrolysis of precursors prepared from Ln(III)-Cr-VI mixed solutions. Only LaCrO4 and NdCrO4 were obtained as a single phase. LaCrO4 was monazite type (monoclinic, P2(1)/n), as reported, and the cell parameters were refined to be a = 0.70369, b = 0.72348, c = 0.66918 nm and beta = 104.950 degrees by an X-ray Rietveld method. NdCrO4 was zircon type (tetragonal, I4(1)/amd) and the eel parameters were a = 0.73107 and c = 0.66999 nm. It was found that CrO43- tetrahedra in LaCrO4 have C-1 symmetry and the four Cr-O bond lengths are different, whereas those in NdCrO4 have D-2d symmetry and all Cr-O bond lengths are 0.1702 nm. Detailed Raman spectra of LaCrO4 and NdCrO4 were measured and assigned to the vibrational modes of the CrO(4)(3-)tetrahedra. Molecular orbital calculations indicated that the charge density on the chromium ions in the tetrahedra is much less than the nominal 5+ due to the migratory electrons from oxygen atoms, and nearly the same irrespective of the symmetry of tetrahedron, suggesting that the Cr-O bonds are strongly covalent in nature.
  • Shimizu, A., Inagaki, M. and Tachikawa, H.: “Dynamics of hydrogen and muonium atoms trapped in diamond crystal”, Solid State Ionics, 127: 157-162 (2000)*
    2000年 [査読無し][通常論文]
  • Tachikawa, H.:” Full dimensional ab-initio dynamics calculations of electron capture processes by the H3O+ ion.”, Phys. Chem. Chem. Phys., 2: 4327-4333 (2000)*
    2000年 [査読無し][通常論文]
  • Tachikawa, H.: ”A full dimensional ab-initio dynamics study on the ionization processes of CF4", J. Phys. B., 33: 2367-2376 (2000)*
    2000年 [査読無し][通常論文]
  • A. Shimizu, A. and H. Tachikawa, H.: “Thermal activation of the trapped proton in diamond crystal: Direct molecular dynamics calculations”, Chem. Phys. Lett., 323: 448-453 (2000)*
    2000年 [査読無し][通常論文]
  • Shimizu, A. and Tachikawa, H.: “Dynamics behavior of lithium in graphite lattice : MD calculation approach” J. Phys. Chem. Solid, 61: 1895-1899 (2000)*
    2000年 [査読無し][通常論文]
  • Tachikawa, H.:”The ionization dynamics of SF6: a full dimensional direct ab-initio dynamics study”, J. Phys. B, 33: 1725-1733 (2000) *.
    2000年 [査読無し][通常論文]
  • Tachikawa, H.: ”Full dimensional ab-initio direct dynamics Calculations of the ionization of H2 clusters (n=3,4, and 6)” Phys. Chem. Chem. Phys., 2: 4702-4707 (2000)*
    2000年 [査読無し][通常論文]
  • T Ichikawa, H Tachikawa, T Kumada, J Kumagai, T Miyazaki
    CHEMICAL PHYSICS LETTERS 307 3-4 283 - 286 1999年07月 [査読無し][通常論文]
     
    Theoretical support for the recent finding of the formation of electron bubbles (excess electrons trapped in vacancies) in crystalline H-2 containing a small amount of D-2 has been given. Quantum-mechanical calculations have shown that the addition of D-2 lowers the energy of the electron bubbles by expanding the volume of the vacancies, which prevents the conversion of the electron bubbles to H-2(-) anions. (C) 1999 Elsevier Science B.V. All rights reserved.
  • C. Maul, C. Dietrich, T. Haas, K-H, Gericke, H. Tachikawa, S.R. Langford, M. Kono, C.L. Reed, R.N. Dixon, and M.N.R. Ashfold,"Ultraviolet photolysis of formyl fluoride: the F+ HCO product channel" Phys. Chem. Chem. Phys., 1, 767 (1999)*
    1999年 [査読無し][通常論文]
  • M. Takayanagi, Y. Kurosaki, Y., and H. Tachikawa, "Ab-initio MO calculations on Potential Energy Surfaces of CCl4", Radiat. Phys. Chem., 55, 367-371 (1999)*
    1999年 [査読無し][通常論文]
  • A. Shimizu and H. Tachikawa, "A direct molecular orbital dynamics study on proton transfer in the diamond lattice", Chem. Phys. Lett., 314, 516-521 (1999)*
    1999年 [査読無し][通常論文]
  • H. Tachikawa, Y. Yamada, and T. Iyama, "Mechanism of silylene extrusion reaction in cyclic polysilane via triplet energy surface: a direct MO dynamics study", Can. J. Chem., 77, 1419-1423 (1999)*
    1999年 [査読無し][通常論文]
  • Ichikawa,T., Tachikawa,H., Kumada, T., Kumagai, J. and Miyazaki, H. "Hydrogen radical anions and electron bubbles in solid hydrogen" Chem. Phys. Lett., 307, 283-286 (1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H., and Shimizu, A., "Classical Dynamics of the Hydrogen atom and Muonium Trapped in Diamond Clusters: A Direct Ab-initio Dynamics Study", Bull. Chem. Soc. Jpn., 72, 1491-1496 (1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H.:"Ionization dynamics of Methanol Dimer: Direct ab-initio dynamics Study", Chem. Phys., 244, 263-272(1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H.:"Electron Localization in Polysilane Radical Ions", J. Phys. Chem. A,103, 2501-2505 (1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H.:"Reaction mechanism of the astrochemical electron capture reaction HCNH+ + e- → HNC + H :A direct ab-initio dynamics study", Phys. Chem. Chem. Phys., 1, 4925-4930 (1999)*.
    1999年 [査読無し][通常論文]
  • Tachikawa, H.:"Photodissociation dynamics of formyl fluoride via the triplet state surface: A direct ab-initio dynamics study", Phys. Chem. Chem. Phys., 1, 2675-2679 (1999)*
    1999年 [査読無し][通常論文]
  • Ichikawa,T., K. Kagei, Ishitani,Y., Tachikawa, H. and Koizumi, H., "Control factors for hydrogen-atom abstraction from organic molecules in cryogenic solids", Radiat. Phys. Chem., 55, 529-534 (1999)*
    1999年 [査読無し][通常論文]
  • Konno,H., Oka,H., Shiba,K., Tachikawa,H. and Inagaki, M., "Carbonization of boron containing polyimide films: B-N bond formation", Carbon, 37, 887-895 (1999)*
    1999年 [査読無し][通常論文]
  • J. Nishihira and H. Tachikawa, "Theoretical Evaluation of a Model of the Catalytic Triands of Serine and Cysteine Proteases by Ab-initio Molecular Orbital Calculation", J. Theor. Biol., 196, 513-519 (1999)*
    1999年 [査読無し][通常論文]
  • A. Shimizu, M. Inagaki and H. Tachikawa, "Temperature effect on the spin density of hydrogen atom trapped in the interstitial site of diamond crystal: a direct molecular orbital dynamics approach", J. Phys. Chem. Solid, 60, 1811-1815 (1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H. and Igarashi,M., "A Direct ab-initio dynamics Study on a gas phase SN2 reaction F- + CH3Cl → FCH3 + Cl- : Dynamics of the near-collinear collision", Chem. Phys. Lett., 303, 81-86 (1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H.:"A Direct MO dynamics Study on the Hydrogen trapped in Crystalline silicon", Chem. Phys. Lett., 300, 577-582 (1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H.:"Ionization dynamics of the Benzene-HF complex: A direct ab-initio dynamics study", J. Phys. Chem. A, 103, 6873-6879 (1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H.:"Mechanism of the product Vibrational-Rotational State Selectivity in a Gas Phase Ion-Molecule Collision O- + HF → OH(V,J) + F-", J. Phys. B, 32, 1451-1458(1999)*
    1999年 [査読無し][通常論文]
  • Tachikawa, H. and Igarashi, M. : "Dynamics of the Ionization Processes of Benzene-H2O Clusters: A direct ab-initio Dynamics Study" J. Phys. Chem. A, 102: 8648-8656 (1998)*
    1998年 [査読無し][通常論文]
  • Igarashi, M. and Tachikawa, H. : "An ab-initio MO Study on the Gas Phase SN2 reaction" Int. J. Mass Spectrom., 181, 151-157 (1998)*
    1998年 [査読無し][通常論文]
  • Shimizu, A. and Tachikawa, H. : "Ab-initio MO Study on the interaction between Alkali matal and dangling bond on Si(111) surface" J. Phys. Chem. Solids., 59: 929-936 (1998)*
    1998年 [査読無し][通常論文]
  • Tachikawa, H.: "Solvation dynamics of fluorenone radical anion by methanol: Direct ab-initio dynamics Study" J. Mol. Struct. (THEOCHEM), 427: 191-198 (1998)*
    1998年 [査読無し][通常論文]
  • Tachikawa, H. : "Photoreaction dynamics of permethylcyclosilane (Me2Si)6 : A direct dynamics study" J. Organometal. Chem., 555: 161-166 (1998)*
    1998年 [査読無し][通常論文]
  • Takayanagi, M., Kurosaki, Y. and Tachikawa, H. : "Application of direct dynamics method to ionization and enectron capturing of CF3Cl" Int. J. Mass Spectrom., 176: 227-235 (1998)*
    1998年 [査読無し][通常論文]
  • Inagaki, M., Tachikawa, H., Nakahashi, T., Konno, H., Higashiyama, Y. : "Chemical Bonding State of Nitrogen in Kapton-Derivated Carbon Film and Its Graphitization Process" Carbon, 36: 1021-1025 (1998)*
    1998年 [査読無し][通常論文]
  • Tachikawa, H. : " Electronic- to- Vibrational and -Rotational Energy Transfer in S(1D) + CO quenching reaction: Ab-initio MO and classical Trajectory Studies" J. Chem. Phys., 108: 3966-3972 (1998)*
    1998年 [査読無し][通常論文]
  • Tachikawa, H. : "Direct ab-initio dynamics Study on the finite temperature effects on the hyperfine coupling constants of a weakly bonded complex" J. Phys. Chem. A, 102: 7065-7069 (1998)*
    1998年 [査読無し][通常論文]
  • Tachikawa H., Igarashi, M. and Komaguchi, K. : "Formation Mechanism of CCl4- Anion in Condensed Phase: A direct ab-initio dynamics study" Int. J. Mass Spectrom., 177: 17-21 (1998)*
    1998年 [査読無し][通常論文]
  • T Ichikawa, H Tachikawa, J Kumagai, T Kumada, T Miyazaki
    JOURNAL OF PHYSICAL CHEMISTRY A 101 40 7315 - 7317 1997年10月 [査読無し][通常論文]
     
    The electron spin resonance g-factor of H-2(-) in gamma-irradiated crystalline H-2 was found to be not 2.003 but 2.0023, A novel model has been proposed for explaining the formation and stabilization of Hz-in crystalline H-2. The model assumes H-2(-) to be located at the center of a cavity that has previously been occupied by a trapped electron. The excess electron of H-2(-) is forced to be attached on one H-2 in the cavity due to strong repulsive interactions between the excess electron and H-2 molecules surrounding the cavity. A quantum mechanical calculation shows that an electron trapped in the vacancy of crystalline Hz automatically converts to H-2(-) by drawing one of the surrounding H-2 molecules into the center of the vacancy.
  • Ichikawa, T., Tachikawa, H., Kumagai, J., Kumada, T. and Miyazaki, T. : "Stabilization of Hydrogen Radical Anions in Solid Hydrogen", J. Phys. Chem. A, 101(40) : 7315-7317 (1997)*
    1997年 [査読無し][通常論文]
  • Tachikawa, H. : "Dynamics of Electron Attachment and Ionization Processes in the CCl4 molecules : An ab-inito MO and Direct Dynamics Study", J. Phys. Chem, A, 101 : 7454-7459 (1997)*
    1997年 [査読無し][通常論文]
  • Tachikawa, H., Ohnishi, K., Hamabayashi, T. and Yoshida, H. : "Translational relaxation of hot O(1D) by collision with N2 molecule : Ab-initio MO and Classical Trajectory Studies", J. Phys. Chem. A, 101 : 2229-2232 (1997)*
    1997年 [査読無し][通常論文]
  • Tachikawa, H. and Komaguchi, K. : "Direct ab-initio dynamics study on the formation of ammonia dimer cations.", J. Mass. Specrom. and Ion process., 164 : 39-44 (1997)*
    1997年 [査読無し][通常論文]
  • Nishihira, J. and Tachikawa, H. : "Theoretical Study on the Interaction between Dopamine and its Receptor by ab-initio MO calculation", J. Theoret. Biology, 185 : 157-163 (1997)*
    1997年 [査読無し][通常論文]
  • Itagaki, M., Shiotani, M. and Tachikawa, H. : "Electronic Structure of Methylacetylene Radical Anion : An ESR and MO Study", Acta. Chim. Scand., 51 : 220-223 (1997)*
    1997年 [査読無し][通常論文]
  • Tachikawa, H. : "Electronic structures of linear polysilane radical anions at ground and low-lying excited states : A theoretical Study", Chem. Phys. Lett., 281 : 221-225 (1997)*
    1997年 [査読無し][通常論文]
  • Tachikawa, H., Iyama, T. and Hamabayashi, T. : "Metal-ligand interactions of the Cu-NO complex at the ground and low-lying excited states : An ab-initio MO study.", Electronic J. Theoret. Chem., 2 : 1-5 (1997)*
    1997年 [査読無し][通常論文]
  • J Kumagai, H Tachikawa, H Yoshida, T Ichikawa
    JOURNAL OF PHYSICAL CHEMISTRY 100 42 16777 - 16778 1996年10月 [査読有り][通常論文]
     
    The measurements of the ESR and optical absorption spectra of polysilane radical ions revealed that the hole in the radical cation is delocalized onto the side chains, whereas the excess electron in the radical anion is confined within the silicon main chain. This observation suggests that the side chains hinder the interchain hopping of the charge for the anion but not the cation. Therefore the hole is the primary charge carrier in polysilanes.
  • "Dynamics of the Vibrational Mode-Specific Proton Transfer Reaction NH +3(v1)+NH3→NH2+NH +4 : ab-initio and Classical Trajectory Studies", Chem. Phys., 211 : 305-312 (1996)*
    1996年 [査読無し][通常論文]
  • "Dynamic Spectral Shifts of Benzophenone Radical Anion Caused by the Solvent Molecule Reorientation. Semiempirical PM3-CI and Classical Trajectory Studies", J. Phys. Chem., 100 : 17090-17093 (1996)*
    1996年 [査読無し][通常論文]
  • "Photodissociation mechanism of ion-molecule complex MgN2+ : ab-initio MO study", J. Mol. Struct. (THEOCHEM), 363 : 263-267 (1996)*
    1996年 [査読無し][通常論文]
  • "Ab-initio MR-SD-CI calculation of the g-tensor compornents of [Cu(H2O)6]2+", Chem. Phys. Lett., 260 : 582-588 (1996)*
    1996年 [査読無し][通常論文]
  • "Electronic structures of linear polysilane radical cations at the ground and low-lying excited states : A theoretical Study", Chem. Phys. Lett., 100 : 17090-17093 (1996)*
    1996年 [査読無し][通常論文]
  • TACHIKAWA H, TSUCHIDA T
    J. Mol. Catal. 96 3 277 - 282 1995年 [査読無し][通常論文]
  • On the hydrogen abstraction reaction CH3 + CH3CN → CH4 + CH2CN. Importance of
    Chem. Phys. Lett. 241 7 - 12 1995年 [査読無し][通常論文]
  • TACHIKAWA H, MURAKAMI A
    J. Phys. Chem. 99 28 11046 - 11050 1995年 [査読無し][通常論文]
  • TACHIKAWA H, HAMABAYASHI T, YOSHIDA H
    J. Phys. Chem. 99 45 16630 - 16635 1995年 [査読無し][通常論文]
  • INAGAKI Y, ABE M, MATSUMI Y, KAWASAKI M, TACHIKAWA H
    J. Phys. Chem. 99 34 12822 - 12828 1995年 [査読無し][通常論文]
  • TACHIKAWA H, KOMATSU E
    Inorg. Chem. 34 26 6546 - 6549 1995年 [査読無し][通常論文]
  • J. Phys. Chem. 99 255 - 261 1995年 [査読無し][通常論文]
  • ICHINOSE N, MIZUNO K, OTSUJI Y, TACHIKAWA H
    Tetrahedron Lett. 35 4 587 - 590 1994年 [査読無し][通常論文]
  • TACHIKAWA H, OHTA N
    Chem. Phys. Lett. 224 5/6 465 - 469 1994年 [査読無し][通常論文]
  • Theoretical study of the vibrational coupling effects on the Isomerization reaction
    J. Mol. Struct.(THEOCHEM) 304 25 - 33 1994年 [査読無し][通常論文]
  • Chem. Phys. 182 185 - 194 1994年 [査読無し][通常論文]
  • TACHIKAWA H, TAKAMURA H, YOSHIDA H
    J. Phys. Chem. 98 20 5298 - 5302 1994年 [査読無し][通常論文]
  • ABE M, INAGAKI Y, SPRINGSTEEN L L, MATSUMI Y, KAWASAKI M, TACHIKAWA H
    J. Phys. Chem. 98 48 12641 - 12645 1994年 [査読無し][通常論文]
  • H TACHIKAWA, H MURAI, H YOSHIDA
    JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS 89 14 2369 - 2373 1993年07月 [査読有り][通常論文]
     
    The geometric structure and electronic state of ion pairs formed by an electron transfer from an alkali metal atom to the C=O group of a carbonyl compound, have been determined using ab initio molecular orbital (MO) and multireference single and double excitation configuration interaction (MRSDCI) methods. As model systems of the ion pair, acetone-Na (AT-Na) and formaldehyde-Na (FA-Na) systems were chosen. The geometry optimizations of the FA-Na ion pair gave two structures as the stable form. One is a linear form with a C-0-Na angle of 168.7-degrees and the other is the pi-form with an angle of 87.6-degrees. The total energies of both ion pairs are similar, although the energy calculation shows that the pi form is slightly more stable than the linear form. On the other hand, the geometry optimization of the AT-Na ion pair gave only a linear form for the stable structure. The MRSDCI wavefunctions of the ion pairs indicate that the interaction between the alkali metal and the carbonyl group is composed of an attractive Coulomb force [C=0-...Na+] at the ground state, whereas the nature of the bonding is determined by the weakly attractive van der Waals force [C=0...Na] at the first excited state. From an analysis of the excited-state wavefunctions, the first absorption band of the ion pairs is assigned to the charge-transfer (CT) transition expressed by pi(C=O)* --> Na(3s). The solvent effects on the spin density of the carbonyl oxygen in a 2-methyltetrahydrofuran (MTHF) matrix were also discussed on the basis of the fractional charge model.
  • TACHIKAWA H, LUND A, OGASAWARA M
    Can. J. Chem. 71 1 118 - 124 1993年 [査読無し][通常論文]
  • 土田猛, 田地川浩人
    表面科学 14 5 272 - 277 1993年 [査読無し][通常論文]
  • TACHIKAWA H, OHTAKE A, YOSHIDA H
    J. Phys. Chem. 97 46 11944 - 11949 1993年 [査読有り][通常論文]
  • TACHIKAWA H, HOKARI N, YOSHIDA H
    J. Phys. Chem. 97 39 10035 - 10041 1993年 [査読有り][通常論文]
  • H KONNO, H TACHIKAWA, A FURUSAKI, R FURUICHI
    ANALYTICAL SCIENCES 8 5 641 - 646 1992年10月 [査読有り][通常論文]
     
    Lanthanum(III) chromium(V) tetraoxide, LaCrO4, was synthesized by a thermal decomposition method and characterized by X-ray photoelectron spectroscopy and ab initio molecular orbital calculations. The chromium (V) state in LaCrO4 is stable in both air and vacuum. The electron binding energies, E(B), and Auger parameters, alpha, of Cr(V) and La(III) indicated that the covalency of the Cr-O bonds in CrO4 tetrahedra is higher than that in CrO6 octahedra of LaCrO3, and that La(III) in LaCrO4 is more ionic than in LaCrO3. The results of ab initio molecular orbital calculations agreed with the measured characteristics, that is, the electrons are flowing from oxygen to Cr(V) and the covalency plays a significant part in the Cr-O bonds. This behavior of the Cr-O bond was considered to contribute to stabilizing CrO43-tetrahedra.
  • H TACHIKAWA, S LUNELL, C TORNKVIST, A LUND
    INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY 43 4 449 - 461 1992年07月 [査読有り][通常論文]
     
    A vibrational coupling model to treat the solvation effects in chemical reaction rate calculations is proposed and applied to the intramolecular hydrogen transfer reaction CH3O. --> .CH2OH in the condensed phase. The effect of solvation is taken into account in two ways: (1) the solvent effect on the activation energy of the reaction is simulated by including 39 surrounding water molecules, represented by fractional charges at the assumed atomic positions, in the potential energy surface calculation; and (2) the vibrational couplings between the 10 nearest solvent molecules and the molecules constituting the reaction system are explicitly included in a vibrational frequency calculation. RRKM theory with Miller's tunneling correction included is employed to calculate the rate constants. The effect of solvation causes a significant change in the chemical reaction rate, mainly through a lowering of the activation energy. The vibrational coupling causes a slight increase of the rate constant in the tunneling region by perturbing the vibrational frequencies of the reactant and transition states, which appear in thc rate-constant expression, but has little effect at higher temperatures.
  • H TACHIKAWA, M SHIOTANI, K OHTA
    JOURNAL OF PHYSICAL CHEMISTRY 96 1 164 - 171 1992年01月 [査読有り][通常論文]
     
    Structure and formation mechanisms of dimer radical cations of methyl- and dimethylacetylene (MA and DMA) have been studied by means of ESR spectroscopy and ab initio MO calculations. Monomer radical cations were generated in halocarbon matrices by ionization radiation at low temperature. It was found that the methylacetylene radical cation, MA+, is stabilized as a complex cation with a chlorine atom of a matrix molecule immediately after irradiation at 77 or 4 K. When the sample was warmed at 105 K in CF2ClCFCl2, the matrix complex cation was converted into a dimer radical cation of methylacetylene, MA2+, characterized by a 9.0-G hyperfine (hf) splitting due to eight hydrogen atoms. Upon further annealing, the dimer cation apparently dissociated, since the propagyl radical, CH2C = CHBAR, could be detected. The dimethylacetylene radical cation was stabilized in the matrix as an isolated monomer cation, DMA+, after irradiation at low temperature. Similar to the MA system, subsequent annealing of DMA+ gave rise to a dimer cation of dimethylacetylene, DMA2+ (9.0 G, 12 H). Comparison of the experimental hf splittings with the results of ab initio MO calculations leads us to conclude that the structures of the both dimer cations, MA2+ and DMA2+, are cyclic, i.e., in the forms of the dimethyl- and tetra-methylcyclobutadiene radical cations, respectively. It is proposed that the formation occurs through a [3+4] cycloaddition reaction of the monomer cation with the parent molecule. The proposed electronic ground states of MA2+ and DMA2+ are 2A2 in C2-upsilon symmetry (two methyl groups in adjacent positions) and 2B2g in D2h symmetry, respectively. The formation mechanisms of these two dimer cations are discussed on the basis of ab initio MO calculations.
  • Structure and Reactivity of PMMA ion radicals - Ab-initio approach
    H. Tachikawa, H. Yoshida and M. Ogasawara
    Radiat. Phys. Chem. 37 107 - 110 1991年 [査読有り][通常論文]
  • ABINITIO MOLECULAR-ORBITAL STUDY ON WATER DIMER ANIONS
    H TACHIKAWA, M OGASAWARA
    JOURNAL OF PHYSICAL CHEMISTRY 94 5 1746 - 1750 1990年03月 [査読有り][通常論文]
  • H TACHIKAWA, T ICHIKAWA, H YOSHIDA
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 112 3 977 - 982 1990年01月 [査読有り][通常論文]
  • H TACHIKAWA, T ICHIKAWA, H YOSHIDA
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 112 3 982 - 987 1990年01月 [査読有り][通常論文]
  • TACHIKAWA H, OGASAWARA M, LINDGREN M, LUND A
    J. Phys. Chem. 92 7 1712 - 1715 1988年 [査読有り][通常論文]

書籍

  • 有機エレクトロニクスの展開
    情報機構 2007年
  • 化学結合の量子論入門
    三共出版 1994年

その他活動・業績

  • Yoshizawa Saori, Abe Shigeaki, Mutoh Mami, Kusaka Teruo, Nakamura Mariko, Yoshida Yasuhiro, Iida Junichiro, Kawabata Hiroshi, Tachikawa Hiroto Jpn. J. Appl. Phys. 56 (1) 2016年11月08日 [査読無し][通常論文]
     
    Oligosilane-functionalized C<inf>60</inf>fullerenes [namely, C<inf>60</inf>–(SiH<inf>2</inf>)<inf>n</inf>–H, n = 1–4] have been investigated by the density functional theory (DFT) method to elucidate the structures and electronic states of oligosilane-radical added fullerene. The DFT calculation showed that oligosilane radicals bind to the carbon atom of C<inf>60</inf>in the on-top site, and a strong Si–C heterojunction is formed. The binding energies of oligosilane radicals to C<inf>60</inf>were calculated to be 24.6–28.2 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The electronic states of oligosilane-functionalized fullerenes C<inf>60</inf>–(SiH<inf>2</inf>)<inf>n</inf>–H are discussed on the basis of theoretical results.
  • Tachikawa Hiroto, Kawabata Hiroshi Jpn. J. Appl. Phys. 55 (6) 2016年04月26日 [査読無し][通常論文]
     
    Functionalized graphenes are known as a high-performance molecular device. In the present study, the structures and electronic states of the aryl radical functionalized graphene have been investigated by the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the mechanism of aryl radical reaction with GR was investigated. The benzene, biphenyl, p-terphenyl, and p-quaterphenyl radicals [denoted by (Bz)<inf>n</inf>(n = 1–4), where n means numbers of benzene rings in aryl radical] were examined as aryl radicals. The DFT calculation of GR–(Bz)<inf>n</inf>(n = 1–4) showed that the aryl radical binds to the carbon atom of GR, and a C–C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol<sup>−1</sup>at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal mol<sup>−1</sup>. The electronic states of GR–(Bz)<inf>n</inf>were examined on the basis of theoretical results.
  • Tachikawa Hiroto Theoretical chemistry accounts 135 (3) 1 -9 2016年02月20日 [査読無し][通常論文]
     
    Ionizing radiation to DNA induces sometimes the DNA damage. In this report, the ionization dynamics of uracil dimer (U)(2) and its water complex (U)(2)-H2O have been investigated by means of direct ab initio molecular dynamics (AIMD) method in order to elucidate the effects of single water molecule on the reaction rate of proton transfer (PT) in DNA model base pair. The (U)(2) dimer is widely used as a simplified mimetic model of Watson-Crick base pair. The static ab initio calculation showed that two conformers exist as neutral complex of (U)(2)-H2O. The direct AIMD calculation of ionization process of (U)(2)-H2O showed that the rate of PT is affected even by a single water molecule, while it was dependent on the position of H2O around (U)(2). The interaction of water molecule with (U)(2) affected the potential energy curve for PT. Especially, the activation barrier along the PT coordinate was significantly changed by the interaction with one H2O molecule. The effects of one H2O molecule on the PT process were discussed on the basis of theoretical results.
  • Abe Shigeaki, Kawano Shimpei, Toida Yu, Nakamura Mariko, Inoue Satoshi, Sano Hidehiko, Yoshida Yasuhiro, Kawabata Hiroshi, Tachikawa Hiroto Jpn. J. Appl. Phys. 55 (3) 2016年01月19日 [査読無し][通常論文]
     
    The structures and electronic states of alkyl-radical-functionalized C<inf>20</inf>fullerenes (denoted by C<inf>20</inf>–R) have been investigated using density functional theory (DFT). The different alkyl radicals investigated were methyl, ethyl, propyl, and butyl radicals. The DFT calculation indicated that the alkyl radical binds to the carbon atom of C<inf>20</inf>in the on-top site, thus forming a strong C–C single bond. The binding energies of the alkyl radicals to C<inf>20</inf>were calculated to be 83.9–86.6 kcal/mol at the CAM-B3LYP/6-311G(d,p) level. The electronic states of the C<inf>20</inf>–R complex are discussed on the basis of the theoretical results.
  • Tachikawa Hiroto, Kawabata Hiroshi International journal of quantum chemistry 116 (2) 123 -129 2016年01月16日 [査読無し][通常論文]
     
    High energy irradiation to the hydrogen bonded system is important in relevance with the initial process of DNA and enzyme damages. In the present study, the effects of radiation to catalytic triad have been investigated by means of direct ab-initio molecular dynamics (AIMD) calculation. As a model of the catalytic triad, Ser-His-Glu residue, which is one of the important enzymes in the acylation reaction, was examined. The ionization and electron attachment processes in Ser-HisGlu were investigated as the radiation effects. The direct AIMD calculation showed that a proton of His is spontaneously transferred to carbonyl oxygen of Glu after the ionization. However, the whole structure of catalytic triad was essentially kept after the ionization. On the other hand, in the case of the electron capture in the model catalytic triad Ser-His-Glu, the dissociation of Glu residue from [Ser-His](2) was found as a product channel. The mechanism of ionization and electron capture process in the catalytic triad was discussed on the basis of theoretical results. (C) 2015 Wiley Periodicals, Inc.
  • Electronic States of Organic Radical-Functionalized Graphenes and Fullerenes: Density Functional Theory (DFT) Study
    Tetsuji Iyama, Hiroshi Kawabata, Takahiro Fukuzumi, Hiroto Tachikawa 2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016年 [査読有り][通常論文]
     
    Structures and electronic states of the aryl radical functionalized graphene have been investigated by means of density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of graphene (GR). Also, the reaction mechanism of aryl radical with GR was investigated. The benzene, biphenyl, pterphenyl, and p-quaterphenyl radicals (denoted by (Bz)n (n=1-4), where n means numbers of benzene rings in aryl radical) were examined as aryl radicals. The DFT calculation of GR-(Bz)n (n=1-4) showed that the aryl radical binds to the carbon atom of GR, and a C-C single bond was formed. The binding energies of aryl radicals to GR were calculated to be ca. 6.0 kcal mol-1 at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists in the aryl radical addition: the barrier heights were calculated to be 10.0 kcal/mol. The electronic states of GR-(Bz) n were discussed on the basis of theoretical results.
  • Molecular Design of Functionalized Fullerenes and Graphenes: Density Functional Theory (DFT) Study
    Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata 2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS) 2016年 [査読有り][通常論文]
  • Tachikawa Hiroto, Kawabata Hiroshi Jpn. J. Appl. Phys. 55 (2) 2015年12月21日 [査読無し][通常論文]
     
    Functionalized fullerenes are known as a high-performance molecules. In this study, the alkyl-functionalized fullerenes (denoted by R–C<inf>60</inf>) have been investigated by means of the density functional theory (DFT) method to elucidate the effects of functionalization on the electronic states of fullerene. Also, the reaction mechanism of alkyl radicals with C<inf>60</inf>was investigated. The methyl, ethyl, propyl, and butyl radicals (denoted by n = 1–4, where n means the number of carbon atoms in the alkyl radical) were examined as alkyl radicals. The DFT calculation showed that the alkyl radical binds to the carbon atom of C<inf>60</inf>at the on-top site, and a strong C–C single bond is formed. The binding energies of alkyl radicals to C<inf>60</inf>were distributed in the range of 31.8–35.1 kcal mol<sup>−1</sup>at the CAM-B3LYP/6-311G(d,p) level. It was found that the activation barrier exists before alkyl addition, the barrier heights were calculated to be 2.1–2.8 kcal mol<sup>−1</sup>. The electronic states of R–C<inf>60</inf>complexes were discussed on the basis of the theoretical results.
  • 五十嵐学, 田地川浩人, 石橋輝雄, 玉城英彦 日本化学会北海道支部研究発表会講演要旨集 2005 118 2005年01月21日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 西平順, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2004 125 2004年01月21日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 西平順, 石橋輝雄 分子構造総合討論会講演要旨集(CD−ROM) 2003 4PA047 2003年09月20日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2003 99 2003年01月31日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 分子構造総合討論会講演要旨集 2002 709 2002年10月01日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 化学反応討論会講演要旨集 18th 120 2002年06月18日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2002 124 2002年01月20日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 分子構造総合討論会講演要旨集 2001 479 2001年09月24日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 日本化学会北海道支部研究発表会講演要旨集 2001 116 2001年01月19日 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 石橋輝雄 分子構造総合討論会講演要旨集 2000 771 2000年09月27日 [査読無し][通常論文]
  • 青木芳尚, 金野英隆, 田地川浩人, 稲垣道夫 日本化学会北海道支部研究発表会講演要旨集 1999 12 1999年02月02日 [査読無し][通常論文]
  • 山田義久, 五十嵐学, 田地川浩人 分子構造総合討論会講演要旨集 1998 156 1998年09月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人 分子構造総合討論会講演要旨集 1998 154 1998年09月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人 化学反応討論会講演要旨集 14th 32 1998年05月 [査読無し][通常論文]
  • 市川恒樹, 田地川浩人, 熊谷純, 熊田高之, 宮崎哲郎 ESR討論会講演要旨集 36th 17 -18 1997年10月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 市川恒樹 フッ素化学討論会講演要旨集 21st 104-105 1997年10月 [査読無し][通常論文]
  • 五十嵐学, 田地川浩人, 市川恒樹 分子構造総合討論会講演要旨集 1997 148 1997年10月 [査読無し][通常論文]
  • Tachikawa, H. : "Electronic Structures of Linear Germane-Silane Copolymer Radical Anions in ground and low-lying excited states : A theoretical Study.", J. Organometal. Chem., 547 : 337-341 (1997)*
    1997年 [査読有り][通常論文]
  • Tachikawa, H. : "Electronic structures of linear polysilane radical cations at ground and low-lying excited states : A theoretical Study", Chem. Phys. Lett., 265 : 455-459 (1997)*
    1997年 [査読有り][通常論文]

共同研究・競争的資金等の研究課題

  • 1) 分子動力学的理論によるナノ機能性分子設計 2) 生体内SN2反応の理論モデリング 3) 特殊反応場クラスター内における反応設計理論 4) 新規な機能をもつ有機・高分子の動力学的分子設計

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