Co-reporter:Hiroto Tachikawa
Chemical Physics 2017 Volume 490(Volume 490) pp:
Publication Date(Web):20 June 2017
DOI:10.1016/j.chemphys.2017.03.012
•The twist angle of the biphenyl radical cation (Bp+) vibrates strongly following hole capture.•The friction of water molecules prevents the twist angle vibration of Bp+.•The amplitude of the Bp+ twist vibration is decreased by water molecules.•Hydration affects the proton-hyperfine coupling constants negligibly.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.Download high-res image (105KB)Download full-size image
Co-reporter:Hiroto Tachikawa, Kazuko Haga, Kazuo Yamada
Computational and Theoretical Chemistry 2017 Volume 1115(Volume 1115) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.comptc.2017.06.009
•Ni ferrocyanide (Ni-FeCN) is an effective adsorbent of radioactive Cs+ in waste solutions.•The binding of K+ to Ni-FeCN is stronger than that of Cs+ if no water molecules are present in the ion-exchange reaction.•The ion-exchange reaction with water is exothermic and proceeds efficiently at room temperature.Since the accident at the Fukushima nuclear power plant, the removal of radioactive cesium ions (137Cs+) from wastewater has become an important topic. Nickel ferrocyanide (Ni-FeCN) is known to adsorb 137Cs+ 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.Download high-res image (113KB)Download full-size image
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
Solid State Sciences 2016 Volume 55() pp:138-143
Publication Date(Web):May 2016
DOI:10.1016/j.solidstatesciences.2016.03.004
•Hydrogen atom can bind to the carbon and boron atoms of BN-CNT without activation barrier.•The activation barrier was found in the approaching of hydrogen atom to the nitrogen atom of BN-CNT.•Charge transfer process is important in the hydrogen addition to the N site of BN-CNT.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.
Co-reporter:Hiroto Tachikawa
Surface Science 2016 Volume 647() pp:1-7
Publication Date(Web):May 2016
DOI:10.1016/j.susc.2015.11.011
•Ionization dynamics of water dimer adsorbed on the ice surface was theoretically investigated.•The calculations were carried out by direct ab-initio MD method combined with ONION technique.•Fast proton transfer was found after the ionization.•It was found that the product complex, H3O+(OH), is separated to H3O + and OH on the ice surface.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.
Co-reporter:Hiroto Tachikawa, Tomoya Takada
Computational and Theoretical Chemistry 2016 Volume 1089() pp:13-20
Publication Date(Web):1 August 2016
DOI:10.1016/j.comptc.2016.05.008
•Two types of proton transfer (PT) processes were observed in water tetramer cations.•Varying the topological conformation affected the PT reaction rate.•Ionizing the cyclic water tetramer resulted in fast PT without an intermediate.•Branched tetramers lead to the formation of long-lived non-PT intermediates.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.
Co-reporter:Hiroto Tachikawa
The Journal of Physical Chemistry A 2016 Volume 120(Issue 37) pp:7301-7310
Publication Date(Web):September 2, 2016
DOI:10.1021/acs.jpca.6b04699
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 50 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.
Co-reporter:Hiroto Tachikawa and Hiroshi Kawabata
The Journal of Physical Chemistry A 2016 Volume 120(Issue 33) pp:6596-6603
Publication Date(Web):August 3, 2016
DOI:10.1021/acs.jpca.6b05563
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 (∼10 K). The effects of single water molecule on the reaction barrier of CO2 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.
Co-reporter:Hiroto Tachikawa and Tomoya Takada
RSC Advances 2015 vol. 5(Issue 9) pp:6945-6953
Publication Date(Web):17 Dec 2014
DOI:10.1039/C4RA14763D
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.
Co-reporter:Hiroto Tachikawa, Hiroshi Kawabata
Solid State Sciences 2015 Volume 48() pp:141-146
Publication Date(Web):October 2015
DOI:10.1016/j.solidstatesciences.2015.08.002
•DFT calculations were carried out for Alkali metal-NTCDA system•Effects of Alkali metals on the band gap of NTCDA were examined.•It was found that the band gap is red-shifted.•Mechanism of specific band gap feature was discussed.Structures and electronic states of organic–inorganic compound of 1,4,5,8-naphthalene-tetracarboxylic-dianhydride (NTCDA) with alkali metals, Mn(NTCDA) (MLi 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 CO double bond character of NTCDA was changed to a C–O single bond like character by the strong interaction of M to the CO and O sites. This change was the origin of the red-shift of the IR spectrum. The UV–vis absorption spectra of Mn(NTCDA) were theoretically predicted on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama
Solid State Sciences 2014 Volume 28() pp:41-46
Publication Date(Web):February 2014
DOI:10.1016/j.solidstatesciences.2013.12.014
•DFT calculations were carried out for fluorinated graphene.•Effects of fluorination on the band gap of graphene were examined.•It was found that the band gap is red-shifted.•Mechanism of specific band gap feature was discussed.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 (DFT) 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.
Co-reporter:Dr. Hiroto Tachikawa
ChemPhysChem 2014 Volume 15( Issue 8) pp:1604-1610
Publication Date(Web):
DOI:10.1002/cphc.201301151
Abstract
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 exothermic, 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 kcal mol−1 (per EC molecule), respectively. The intermolecular distances between Li+ and the F atom of BF4− are elongated: 1.773 Å (n=0), 1.820 Å (n=1), 1.974 Å (n=2), 1.942 Å (n=3), and 4.156 Å (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)4Li+−(BF4−). The reaction mechanism is discussed on the basis of the theoretical results.
Co-reporter:Tetsuji Iyama;Hiroshi Kawabata
Journal of Solution Chemistry 2014 Volume 43( Issue 9-10) pp:1676-1686
Publication Date(Web):2014 October
DOI:10.1007/s10953-014-0228-6
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 54.2° for two phenyl rings (referred to as ϕ). 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 (ϕ = 55.1° 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–π* transition (S1 state) is blue-shifted by the solvation, whereas two π–π* transitions (S2 and S3) were red-shifted. The origin of the specific spectral shifts is discussed on the basis of the theoretical results.
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
Thin Solid Films 2014 Volume 554() pp:199-203
Publication Date(Web):3 March 2014
DOI:10.1016/j.tsf.2013.08.108
•Density functional theory calculations were carried out for hydrogen on graphene•Effects of hydrogenation on the band gap of graphene were examined.•The band gap showed a minimum at a finite coverage.•Mechanism of specific band gap feature was discussed.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 (γ = 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.
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama
Thin Solid Films 2014 Volume 554() pp:148-153
Publication Date(Web):3 March 2014
DOI:10.1016/j.tsf.2013.08.020
•Hydrogen atom addition to C60 was investigated.•First hydrogen atom addition proceeded with very low activation barrier.•Second hydrogen addition was dependent on the binding site.•Addition site of second atom was correlated with spin density.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 (C60) 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 C60-H were discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa
The Journal of Physical Chemistry A 2014 Volume 118(Issue 18) pp:3230-3236
Publication Date(Web):April 16, 2014
DOI:10.1021/jp5014175
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 Cs 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)···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.
Co-reporter:Hiroto Tachikawa;Takahiro Fukuzumi
Journal of Solution Chemistry 2014 Volume 43( Issue 9-10) pp:1519-1528
Publication Date(Web):2014 October
DOI:10.1007/s10953-014-0167-2
Electron detachment dynamics of the hydrated superoxide anion \( {\text{O}}_2^ - ({\text{H}}_{ 2} {\text{O}})_{n}\) (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 O2 + 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 O2(3Σ) 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.
Co-reporter:Hiroto Tachikawa, Shigeaki Abe
Electrochimica Acta 2014 120() pp: 57-64
Publication Date(Web):
DOI:10.1016/j.electacta.2013.12.054
Co-reporter:Hiroto Tachikawa, Tomoya Takada
Chemical Physics 2013 Volume 415() pp:76-83
Publication Date(Web):29 March 2013
DOI:10.1016/j.chemphys.2012.12.027
Abstract
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 ∼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.
Co-reporter:Hiroto Tachikawa
RSC Advances 2012 vol. 2(Issue 17) pp:6897-6904
Publication Date(Web):30 May 2012
DOI:10.1039/C2RA20246H
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 π-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 π-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.
Co-reporter:Hiroto Tachikawa, Hiroshi Kawabata
Journal of Organometallic Chemistry 2012 720() pp: 60-65
Publication Date(Web):
DOI:10.1016/j.jorganchem.2012.07.002
Co-reporter:Tomoya Takada, Hiroshi Kawabata, Hiroto Tachikawa
Journal of Molecular Structure 2012 1020() pp: 1-5
Publication Date(Web):
DOI:10.1016/j.molstruc.2012.04.005
Co-reporter:Hiroto Tachikawa and Takahiro Fukuzumi
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 13) pp:5881-5887
Publication Date(Web):17 Feb 2011
DOI:10.1039/C0CP01542C
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.
Co-reporter:Hiroto Tachikawa
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 23) pp:11206-11212
Publication Date(Web):13 May 2011
DOI:10.1039/C0CP02861D
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, 2A′′ and 2A′) 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 2A′′ state, a proton transfer complex H3O+(OH) is only formed as a long-lived complex. On the other hand, in the ionization to the 2A′ 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 2A′′ 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.
Co-reporter:Hiroto Tachikawa, Akihiro Yabushita and Masahiro Kawasaki
Physical Chemistry Chemical Physics 2011 vol. 13(Issue 46) pp:20745-20749
Publication Date(Web):17 Oct 2011
DOI:10.1039/C1CP20649D
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, 1B1 ← 1A1, 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.
Co-reporter:Hiroto Tachikawa
Chemical Physics Letters 2011 Volume 513(1–3) pp:94-98
Publication Date(Web):6 September 2011
DOI:10.1016/j.cplett.2011.07.074
Abstract
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.
Co-reporter:Hiroto Tachikawa
The Journal of Physical Chemistry A 2011 Volume 115(Issue 33) pp:9091-9096
Publication Date(Web):July 17, 2011
DOI:10.1021/jp202778t
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 Cs 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.
Co-reporter:Hiroto Tachikawa;Hiroshi Kawabata
Theoretical Chemistry Accounts 2011 Volume 128( Issue 2) pp:207-213
Publication Date(Web):2011 January
DOI:10.1007/s00214-010-0822-7
Solvent re-orientation process of triplet acetone/methanol complex and intermolecular hydrogen atom abstraction reaction on the triplet state energy surface, (CH3)2C=O (T1) + CH3OH → (CH3)2C–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 T1 state showed that the transition state is 16.4 and 30.9 kcal/mol lower than the energy levels of S1 and S2 states, respectively, and 9.2 kcal/mol higher than the bottom of T1 state. The product state, (CH3)2C–OH⋯CH2OH, is 8.4 kcal/mol lower in energy than the level of T1 state. The direct ab initio MD calculation showed that the product is rapidly formed within 150 fs and the separated products (CH3)2C–OH + CH2OH were formed. The mechanism of reaction dynamics of the triplet acetone/methanol complex was discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Yoshinori Nagoya, Takahiro Fukuzumi
Journal of Power Sources 2010 Volume 195(Issue 18) pp:6148-6152
Publication Date(Web):15 September 2010
DOI:10.1016/j.jpowsour.2010.01.014
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.
Co-reporter:Hiroto Tachikawa, Takahiro Fukuzumi, Kazushige Inaoka and Inosuke Koyano
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 47) pp:15399-15405
Publication Date(Web):2010/10/26
DOI:10.1039/C004202A
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, 2E and 2A1 of the CH3CN+ primary ion. The cross section for PT of the 2A1 state was smaller than that of the 2E 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 2E state than that in the 2A1 state. The direct ab initio molecular dynamics (MD) calculations showed that two mechanisms, direct proton transfer and complex formation, contribute the reaction dynamics.
Co-reporter:Hiroto Tachikawa and Shigeaki Abe
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 15) pp:3904-3909
Publication Date(Web):2010/02/24
DOI:10.1039/B923310E
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.
Co-reporter:Hiroto Tachikawa
The Journal of Physical Chemistry A 2010 Volume 114(Issue 14) pp:4951-4956
Publication Date(Web):March 19, 2010
DOI:10.1021/jp100588z
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 HOO 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.
Co-reporter:Hiroto Tachikawa
The Journal of Physical Chemistry A 2010 Volume 114(Issue 37) pp:10309-10314
Publication Date(Web):August 19, 2010
DOI:10.1021/jp105731u
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.
Co-reporter:Hiroto Tachikawa, Yoshinori Nagoya and Hiroshi Kawabata
Journal of Chemical Theory and Computation 2009 Volume 5(Issue 8) pp:2101-2107
Publication Date(Web):July 6, 2009
DOI:10.1021/ct900151s
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.
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama and Kohichi Kato
Physical Chemistry Chemical Physics 2009 vol. 11(Issue 28) pp:6008-6014
Publication Date(Web):28 May 2009
DOI:10.1039/B905173B
Direct ab initio molecular dynamics (MD) method has been applied to a benzophenone–water 1:1 complex Bp(H2O) and free benzophenone (Bp) to elucidate the effects of zero-point energy (ZPE) vibration and temperature on the absorption spectra of Bp(H2O). The n–π* transition of free-Bp (S1 state) was blue-shifted by the interaction with a water molecule, whereas three π–π* transitions (S2, S3 and S4) were red-shifted. The effects of the ZPE vibration and temperature of Bp(H2O) increased the intensity of the n–π* transition of Bp(H2O) and caused broadening of the π–π* transitions. In case of the temperature effect, the intensity of n–π* transition increases with increasing temperature. The electronic states of Bp(H2O) were discussed on the basis of the theoretical results.
Co-reporter:Hiroto Tachikawa and Hiroshi Kawabata
The Journal of Physical Chemistry C 2009 Volume 113(Issue 18) pp:7603-7609
Publication Date(Web):April 8, 2009
DOI:10.1021/jp900365h
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 π-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.
Co-reporter:Tomoya Takada, Hiroto Tachikawa
Journal of Molecular Catalysis A: Chemical 2009 311(1–2) pp: 54-60
Publication Date(Web):
DOI:10.1016/j.molcata.2009.06.022
Co-reporter:Hiroto Tachikawa
Physical Chemistry Chemical Physics 2008 vol. 10(Issue 16) pp:2200-2206
Publication Date(Web):03 Mar 2008
DOI:10.1039/B718017A
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−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].
Co-reporter:Hiroto Tachikawa, Hiroshi Kawabata
Chemical Physics Letters 2008 Volume 462(4–6) pp:321-326
Publication Date(Web):10 September 2008
DOI:10.1016/j.cplett.2008.07.107
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 (TT). After the hole capture of (TT), one of the C–C bonds was preferentially broken, while the structure of (TT)+ 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.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 (TT). After the hole capture of (TT), one of the C–C bonds was preferentially broken, while the structure of (TT)+ 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.
Co-reporter:Hiroto Tachikawa and Hiroshi Kawabata
The Journal of Physical Chemistry B 2008 Volume 112(Issue 24) pp:7315-7319
Publication Date(Web):May 27, 2008
DOI:10.1021/jp801564t
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 (C5−C5′ and C6−C6′ bonds) at the neutral state, which is expressed by (T)2. After the electron capture of (T)2, the C5−C5′ 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.
Co-reporter:Hiroto Tachikawa and Andrew J. Orr-Ewing
The Journal of Physical Chemistry A 2008 Volume 112(Issue 46) pp:11575-11581
Publication Date(Web):October 28, 2008
DOI:10.1021/jp806114y
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 Cs, staggered Cs and C2v 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 + H2 (II). Channel II occurred only from structures very close to the s-Cs 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 H2. 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.
Co-reporter:Hiroto Tachikawa
The Journal of Physical Chemistry C 2008 Volume 112(Issue 27) pp:10193-10199
Publication Date(Web):June 12, 2008
DOI:10.1021/jp800398y
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 AM1 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 (∼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 Cδ+−Fδ-. 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.
Co-reporter:Tetsuji Iyama, Hiroshi Kawabata, Hiroto Tachikawa
Thin Solid Films 2008 Volume 516(Issue 9) pp:2611-2614
Publication Date(Web):3 March 2008
DOI:10.1016/j.tsf.2007.04.140
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. B, 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, 37, 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 Å 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.
Co-reporter:Hiroto Tachikawa, Hiroshi Kawabata
Thin Solid Films 2008 Volume 516(Issue 10) pp:3287-3293
Publication Date(Web):31 March 2008
DOI:10.1016/j.tsf.2007.08.108
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.
Co-reporter:Hiroto Tachikawa, Shigeaki Abe
Chemical Physics Letters 2006 Volume 432(4–6) pp:409-413
Publication Date(Web):11 December 2006
DOI:10.1016/j.cplett.2006.10.110
The excitation energies of O3–H2O complex have been calculated by means of SAC–CI method to elucidate the spectral shifts of excitation energies of O3 caused by the complex formation with a water molecule. The eclipsed form, where the center oxygen of O3 and water oxygen are located on the Cs molecular plane, was examined in the present study. The first and third excitation energies of O3 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 O3–H2O complex occurs efficiently as well as free ozone molecule. The electronic states of the complex was discussed on the basis of theoretical results.The excitation energies of O3–H2O complex have been calculated by means of SAC–CI method to elucidate the spectral shifts of excitation energies of O3 caused by the complex formation with a water molecule. The first and third excitation energies of O3 were slightly blue-shifted by the complex formation with H2O. The electronic states of the complex was discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Manabu Igarashi
Chemical Physics 2006 Volume 324(2–3) pp:639-646
Publication Date(Web):31 May 2006
DOI:10.1016/j.chemphys.2005.12.002
Abstract
Direct ab initio molecular dynamics (MD) calculations have been applied to a SN2 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 Å). The reaction mechanism is discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Hiroshi Kawabata, Kenji Ishida, Kazumi Matsushige
Journal of Organometallic Chemistry 2005 Volume 690(Issue 12) pp:2895-2904
Publication Date(Web):15 June 2005
DOI:10.1016/j.jorganchem.2005.03.003
The structures and electronic states of phenyl-capped terthiophene (denoted by P3T) and the ionic species of P3T have been investigated by means of density functional theory (DFT) and direct MO dynamics calculations. P3T is one of the high-performance molecular devices, which has been utilized as a semi-conductor. The calculations indicated that the neutral P3T has a non-planar structure whose the phenyl rings in both ends of thiophene chain are largely deviated from the molecular plane. The cation and anion radicals, dication and dianion were considered as its ionic states. The structure for cation radical of P3T is close to more planar than that of neutral P3T. The structures for anion radical, dication and dianion take a pure planar structure. The first excitation energy of neutral P3T is calculated to be 2.90 eV at the TD-B3LYP/6-31G(d)//B3LYP/6-311+G(d) level, while the P3T cation and anion radicals have lower excitation energies (1.22 and 1.10 eV, respectively). The direct MO dynamics calculation showed that neutral, cation and anion hold near planar structure at 300 K. On the other hand, oligothiophene (n = 5) and its ionic species are strongly deformed from the planar structure, and thiophene rings in both ends of chain rotate rapidly by thermal activation. The mechanism of the electron conductivity in P3T was discussed on the basis of theoretical results.The structures and electronic states of phenyl-capped terthiophene (denoted by P3T) and the ionic species of P3T have been investigated by means of density functional theory (DFT) and direct MO dynamics calculations. P3T is one of the high-performance molecular devices, which has been utilized as a semi-conductor.
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama, Hiroshi Kawabata
Journal of Molecular Structure: THEOCHEM 2005 Volume 718(1–3) pp:117-122
Publication Date(Web):31 March 2005
DOI:10.1016/j.theochem.2004.11.041
Hybrid density functional theory (DFT) calculations have been carried out for the nitric oxide NO molecule on the Cu model cluster in order to shed light on the diffusion mechanism of the NO molecule on the Cu(100) cluster model surface. The metal surface was represented approximately by a finite metal cluster Cu9. Three binding sites, ‘two-fold site’, ‘four-fold site’, and ‘on-top site’, were considered in the present study. In two-fold site, NO binds to two Cu atoms in the shorter Cu–Cu bond of the surface, whereas NO in four-fold site was bound in the longer Cu–Cu bond and interacts with four Cu atoms. The binding energies of NO were larger in the order, on-top
Co-reporter:Hiroto Tachikawa, Hiroshi Kawabata
Journal of Photochemistry and Photobiology B: Biology 2005 Volume 79(Issue 3) pp:191-195
Publication Date(Web):1 June 2005
DOI:10.1016/j.jphotobiol.2005.01.004
Effects of the residues on the excitation energies of protonated Schiff base of retinal (PSBR) in bacteriorhodopsin have been investigated by means of time-dependent density functional theory. The residues around PSBR are replaced by the point charges on atoms. The structures of PSBR and residues are referred from X-ray data. The atomic charges on the each residue were calculated the B3LYP/6-311G(d,p) level. The excitation energy of PSBR perturbed by the point charges on atoms of each residue was calculated at the B3LYP/6-31G(d,p) level. A total of 23 residues and five water molecules around PSBR were considered in the calculations. The large spectral shifts were caused by the Asp212 and Asp85. The origin of the spectral shifts was discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Manabu Igarashi, Jun Nishihira, Teruo Ishibashi
Journal of Photochemistry and Photobiology B: Biology 2005 Volume 79(Issue 1) pp:11-23
Publication Date(Web):4 April 2005
DOI:10.1016/j.jphotobiol.2004.11.015
Ab initio molecular orbital (MO) and hybrid density functional theory (DFT) calculations have been applied to the initial step of the acylation reaction catalyzed by acetylcholinesterase (AChE), which is the nucleophiric addition of Ser200 in catalytic triads to a neurotransmitter acetylcholine (ACh). We focus our attention mainly on the effects of oxyanion hole and Glu327 on the potential energy surfaces (PESs) for the proton transfer reactions in the catalytic triad Ser200–His440–Glu327. The activation barrier for the addition reaction of Ser200 to ACh was calculated to be 23.4 kcal/mol at the B3LYP/6-31G(d)//HF/3-21G(d) level of theory. The barrier height under the existence of oxyanion hole, namely, Ser200–His440–Glu327–ACh–(oxyanion hole) system, decreased significantly to 14.2 kcal/mol, which is in reasonable agreement with recent experimental value (12.0 kcal/mol). Removal of Glu327 from the catalytic triad caused destabilization of both energy of transition state for the reaction and tetrahedral intermediate (product). PESs calculated for the proton transfer reactions showed that the first proton transfer process is the most important in the stabilization of tetrahedral intermediate complex. The mechanism of addition reaction of ACh was discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama
Journal of Photochemistry and Photobiology B: Biology 2004 Volume 76(1–3) pp:55-60
Publication Date(Web):25 October 2004
DOI:10.1016/j.jphotobiol.2004.07.005
One-dimensional potential energy curves for the isomerization of protonated Schiff base of retinal (PSBR) in bacteriorhodopsin (bR), i.e., isomerization from all-trans- to 13-cis-forms, have been calculated by means of time-dependent density functional theory (TD-DFT) calculations, in order to elucidate the mechanism of initial step in photo-absorption. The transition state of the isomerization in the first excited state is located at θ13–14 = 58°, where θ13–14 means twist angle around the C13C14 double bond of PSBR The potential barrier is formed by the avoided crossing between S1 (Bu-like) and S2 (Ag-like) states. The mechanism of the isomerization was discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa and Hiroshi Kawabata
Journal of Materials Chemistry A 2003 vol. 13(Issue 6) pp:1293-1297
Publication Date(Web):24 Apr 2003
DOI:10.1039/B301913F
Ab-initio DFT and configuration interaction (CI) calculations have been carried out for indium–carbonyl compounds, such as acetone–In (Ac–In), 1,8-naphthalic anhydride–In (In2NA) and 3,4,9,10-perylenetetracarboxylic dianhydride–indium (In4PTCDA), in order to shed light on the mechanism of electronic conductivity in the molecular devices. It was found that the electronic state of these complexes at the ground state is composed of ion-pair states expressed approximately by (Acδ−)(Inδ+), (In2)δ+(NA)δ− and (In4)δ+(PTCDA)δ−, respectively. On the other hand, the interaction at the first excited state was changed to a van der Waals interaction. Namely, the electron returned again to the In atom by electronic excitation. The second excited state is attributed to internal excitation within the carbonyl anion, while the charge on the indium was close to neutral. The mechanism of the electronic conductivity was discussed on the basis of theoretical results.
Co-reporter:Hiroshi Kawabata and Hiroto Tachikawa
Physical Chemistry Chemical Physics 2003 vol. 5(Issue 17) pp:3587-3590
Publication Date(Web):24 Jul 2003
DOI:10.1039/B305062A
Structures and electronic states of a molecular complex formed between fluorenone and sodium atom (denoted by FL–Na) have been investigated by means of ab initio density functional theory (DFT). The most stable structure of FL–Na has a Cs symmetry where the sodium atom is located on the Cs plane perpendicular to the molecular plane of FL where all atoms are located. The sodium atom binds to the carbonyl oxygen of FL and the angle of Na–O–C is calculated to be 157° at the B3LYP/6-311+G(d) level. The charge on the Na atom shows a positive value (∼+0.80), and unpaired electron is delocalized over the FL molecule, indicating that the FL–Na complex exists as an ion-pair state expressed by (CO)δ−(Na)δ+ at the ground state (δ∼+0.80). The proton hyperfine coupling constants and excitation energies calculated at the B3LYP/6-311+G(d) and B3LYP/6-31++G(d,p) levels are in good agreement with previous experiments. The electronic states at the ground and first excited states were discussed.
Co-reporter:Hiroto Tachikawa, Hiroshi Kawabata
Journal of Organometallic Chemistry 2003 Volume 678(1–2) pp:56-60
Publication Date(Web):15 July 2003
DOI:10.1016/S0022-328X(03)00404-2
The structures and electronic states of acetone–metal complexes (Ac–M, where M=Ga, Al, and B) have been calculated by means of ab-initio DFT and configuration interaction (CI) calculations in order to shed light on the mechanism of the electron conductivity and doping effects. It was found that the electronic states of Ac–Ga and Ac–Al at the ground state are composed of ion-pair state expressed approximately by (Acδ−)(Mδ+): the electron is transferred from metal to the carbonyl group, suggesting that the carbonyl compound interacting with Ga and Al behaves as an n-type semiconductor. In the case of the Ac–B complex, on the other hand, the electron on Ac is significantly transferred to the boron atom, expecting that hole is transferred in the boron-doped carbonyl compound (p-type semiconductor). In these complexes, the first electronic transition is a charge-transfer band between metal and carbonyl group. The mechanism of the electronic conductivity was discussed on the basis of theoretical results.The structures and electronic states of acetone–metal complexes (Ac–M, where M=Ga, Al, and B) have been investigated using ab-initio DFT and CI calculations in order to elucidate the mechanism of the electron conductivity and doping effects. It was found that the electronic states of Ac–Ga and Ac–Al at the ground state are composed of ion-pair state expressed approximately by (Acδ−)(Mδ+).
Co-reporter:Hiroto Tachikawa and Tetsuji Iyama
Physical Chemistry Chemical Physics 2002 vol. 4(Issue 23) pp:5806-5812
Publication Date(Web):24 Oct 2002
DOI:10.1039/B207927P
Electron detachment dynamics of the benzophenone anion–water complex Bp−(H2O) have been investigated by means of full dimensional direct ab-initio trajectory calculation. The structural relaxation process of the neutral complex Bp(H2O) following the vertical electron detachment of Bp−(H2O), which is expressed by [Bp(H2O)]ver→[Bp(H2O)]solv, was calculated by the direct ab-initio trajectory calculations, where [Bp(H2O)]ver and [Bp(H2O)]solv mean the Bp(H2O) neutral complex having a structure at vertical electron detachment point from the Bp−(H2O) anion complex and a relaxation structure of Bp(H2O), respectively. From the dynamics calculations, it was found that the solvation structure of Bp(H2O) is drastically changed to [Bp(H2O)]solv after the electron detachment of Bp−(H2O). According to the structural relaxation including the solvent re-orientation around the benzophenone, the excitation energies for both nπ* and ππ* transitions were blue-shifted as a function of time. The mechanism of the electron detachment process was discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa
Physical Chemistry Chemical Physics 2002 vol. 4(Issue 24) pp:6018-6026
Publication Date(Web):13 Nov 2002
DOI:10.1039/B207635G
Ionization processes of benzene–ammonia 1∶1 complex (BzNH3) have been investigated by means of full dimensional direct ab-initio trajectory, ab-initio molecular orbital (MO) and density functional theory (DFT) calculations. The static ab-initio MO calculations showed that a dipole of NH3 orients toward the center-of-mass of Bz in a stable structure of BzNH3. Trajectories on the potential energy surfaces (PESs) for the ground and first excited states of BzNH+3, expressed schematically by Bz(NH+3) and (Bz+)NH3, respectively, were calculated at the UHF/4-21G(d) level. The calculations for the (Bz+)NH3 state indicated that two reaction channels are competitive with each other as product channels. One is the dissociation channel in which the NH3 molecule is directly dissociated from Bz+. The other one is complex formation channel in which the trajectory leads to a strongly bound complex where NH3 is bound to one of the carbon atoms of Bz+ and a N–C bond is newly formed. On the other hand, a weakly bound complex composed of Bz and NH+3 was formed in the ionization to the Bz(NH+3) state. A hydrogen of NH+3 orients toward one of the carbon atoms of Bz. The dissociation product (Bz+NH+3) was not obtained in this state. The mechanism of the ionization of BzNH3 is discussed on the basis of the theoretical results.
Co-reporter:Hiroto Tachikawa, Manabu Igarashi, Teruo Ishibashi
Chemical Physics Letters 2002 Volume 363(3–4) pp:355-361
Publication Date(Web):9 September 2002
DOI:10.1016/S0009-2614(02)01211-3
Direct ab initio trajectory calculations have been applied to a typical microsolvated SN2 reaction F−(H2O)+CH3Cl at hyperthermal collision energies. The branching ratios for the product channels,were calculated as a function of center-of-mass collision energy (Ecoll). It was found that branching ratios of the product channels were drastically changed by the increase of Ecoll. At the collision energy of 30 kcal/mol, the branching ratios of channels I:II:III were calculated to be 0.37, 0.53, and 0.10, respectively. The branching ratio for channel II became 0.69 at collision energy of 40 kcal/mol, meaning that channel II is dominant at higher collision energies, although the ratio of channel II was close to zero at thermal energy. These results suggested that the product channels in the microsolvated SN2 reaction are significantly affected by the collision energy.
Co-reporter:Hiroto Tachikawa, Manabu Igarashi, Teruo Ishibashi
Chemical Physics Letters 2002 Volume 352(1–2) pp:113-119
Publication Date(Web):24 January 2002
DOI:10.1016/S0009-2614(01)01427-0
Temperature effects on the hyperfine coupling constants (hfcc's) of the methyl radical have been investigated by means of direct ab initio molecular dynamics (MD) method. The calculations showed that the hydrogen-hfcc (H-hfcc) of CH3 increases with increasing temperature. Also, it was indicated that hfcc of the carbon atom of CH3 increases as temperature is increased. The H-hfcc's of CH3 were varied from −22.94 to −22.77 G in the temperature ranges 10–300 K. These features were in good agreement with electron paramagnetic resonance (EPR) experiments. The effects of temperature on H-hfcc were discussed on the basis of theoretical results.
Co-reporter:Manabu Igarashi, Teruo Ishibashi, Hiroto Tachikawa
Journal of Molecular Structure: THEOCHEM 2002 Volume 594(1–2) pp:61-69
Publication Date(Web):11 October 2002
DOI:10.1016/S0166-1280(02)00338-X
Temperature and solvation effects on the hyperfine coupling constants (HFCCs) of methyl radical have been investigated by means of direct ab initio molecular dynamics (MD) method. The complexes composed of methyl radical and H2O molecules, CH3(H2O)n (n=0–2), were chosen as models of the solvation systems. The geometry optimizations of CH3(H2O) showed that the hydrogen of H2O molecule orients toward the carbon of CH3, and it is weakly bound to the carbon atom of CH3. The binding energies for n=1 and n=2 were calculated to be 1.50 and 2.82 kcal/mol at the MP2/6-311++G(d,p) level, respectively. The direct ab initio MD calculations indicated large temperature dependence of HFCCs: hydrogen-HFCC of CH3 decreases with increasing temperature. This large change is due to the fact that the structure of the complex is flexible and is significantly varied by thermal activation. Mechanism of the temperature dependence of HFCCs was discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Manabu Igarashi and Teruo Ishibashi
Physical Chemistry Chemical Physics 2001 vol. 3(Issue 15) pp:3052-3056
Publication Date(Web):29 Jun 2001
DOI:10.1039/B102698B
Structure and vibrational frequencies of the benzene–water complex cation [BzH2O]+ have been calculated by means of density functional theory (B3LYP calculation). A planar structure with a Cs symmetry, in which all heavy atoms are located on a molecular plane, was obtained as the most stable form of the [BzH2O]+ cation. Hydrogen atoms of the water molecule are located above and below the molecular plane. From the present calculations, it was predicted that vibrational frequencies of symmetric and asymmetric O–H stretching modes of H2O (ν1 and ν3 modes, respectively) are red-shifted from those of a free H2O by the formation of a complex, whereas the H–O–H bending mode (ν2 mode) is blue-shifted. Infrared intensities of the three modes of H2O
were significantly increased by the complex formation. Similar features were obtained for the ethylene–H2O complex cation [C2H4–H2O]+. The origin of the frequency-shifts is discussed on the basis of theoretical results. The hydrogen-hyperfine coupling constants of the complex cations were also predicted theoretically.
Co-reporter:Manabu Igarashi, Hiroto Tachikawa
International Journal of Mass Spectrometry 2000 Volume 197(1–3) pp:243-252
Publication Date(Web):29 February 2000
DOI:10.1016/S1387-3806(99)00261-4
Direct ab initio dynamics calculations on the photoelectron detachment processes of H3O− anion have been carried out by using HF/6-311G∗∗ full dimensional potential energy surface (PES). Total energy and the energy gradient of atoms were calculated in each time step. The excess energy was assumed to be zero at the starting point of the trajectory. The H3O− anion is composed of two isomers, H−(H2O) and OH−(H2) in which H− and OH− anions are solvated by H2O and H2 molecules, respectively. The present calculations indicated that the available energy, yielded by the electron detachment of H−(H2O), is almost distributed into the relative translational energy between fragments. On the other hand, the available energy in an OH−(H2) isomer is partitioned into both the relative translational mode and internal modes of the fragments, although the latter energy is minor. The excitation of internal modes of the products were observed for only the detachment process of the OH−(H2) complex. These are due to the fact that the structure of solvent molecules (H2O and H2) in each complex is significantly close to that of free molecules whereas the PES of the neutral state is always repulsive. The mechanism of the electron detachment process of H3O− is discussed on the basis of theoretical results.
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama, Shigeaki Abe
Physics Procedia (2011) Volume 14() pp:139-142
Publication Date(Web):1 January 2011
DOI:10.1016/j.phpro.2011.05.027
The interaction of OH radical with C60 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 C60 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 sp2 to sp3-like hybridization occurs easily by the approach of OH. The unpaired electron is distributed widely over the C60 surface in the C60(OH) complex.
Co-reporter:Hiroto Tachikawa
Physical Chemistry Chemical Physics 2008 - vol. 10(Issue 16) pp:NaN2206-2206
Publication Date(Web):2008/03/03
DOI:10.1039/B718017A
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−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].
Co-reporter:Hiroto Tachikawa, Tetsuji Iyama and Kohichi Kato
Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 28) pp:NaN6014-6014
Publication Date(Web):2009/05/28
DOI:10.1039/B905173B
Direct ab initio molecular dynamics (MD) method has been applied to a benzophenone–water 1:1 complex Bp(H2O) and free benzophenone (Bp) to elucidate the effects of zero-point energy (ZPE) vibration and temperature on the absorption spectra of Bp(H2O). The n–π* transition of free-Bp (S1 state) was blue-shifted by the interaction with a water molecule, whereas three π–π* transitions (S2, S3 and S4) were red-shifted. The effects of the ZPE vibration and temperature of Bp(H2O) increased the intensity of the n–π* transition of Bp(H2O) and caused broadening of the π–π* transitions. In case of the temperature effect, the intensity of n–π* transition increases with increasing temperature. The electronic states of Bp(H2O) were discussed on the basis of the theoretical results.
Co-reporter:Hiroto Tachikawa
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 23) pp:NaN11212-11212
Publication Date(Web):2011/05/13
DOI:10.1039/C0CP02861D
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, 2A′′ and 2A′) 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 2A′′ state, a proton transfer complex H3O+(OH) is only formed as a long-lived complex. On the other hand, in the ionization to the 2A′ 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 2A′′ 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.
Co-reporter:Hiroto Tachikawa, Takahiro Fukuzumi, Kazushige Inaoka and Inosuke Koyano
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 47) pp:NaN15405-15405
Publication Date(Web):2010/10/26
DOI:10.1039/C004202A
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, 2E and 2A1 of the CH3CN+ primary ion. The cross section for PT of the 2A1 state was smaller than that of the 2E 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 2E state than that in the 2A1 state. The direct ab initio molecular dynamics (MD) calculations showed that two mechanisms, direct proton transfer and complex formation, contribute the reaction dynamics.
Co-reporter:Hiroto Tachikawa and Shigeaki Abe
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 15) pp:NaN3909-3909
Publication Date(Web):2010/02/24
DOI:10.1039/B923310E
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.
Co-reporter:Hiroto Tachikawa and Takahiro Fukuzumi
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 13) pp:NaN5887-5887
Publication Date(Web):2011/02/17
DOI:10.1039/C0CP01542C
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.
Co-reporter:Hiroto Tachikawa, Akihiro Yabushita and Masahiro Kawasaki
Physical Chemistry Chemical Physics 2011 - vol. 13(Issue 46) pp:NaN20749-20749
Publication Date(Web):2011/10/17
DOI:10.1039/C1CP20649D
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, 1B1 ← 1A1, 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.
