Browsing by Author "Hayashi, M."

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Density Functional Theory Study of Conformation-Dependent Properties of Neutral and Radical Cationic L-Tyrosine and L-Tryptophan
(2011-09-01)
Baek, K. Y.
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Fujimura, Y.
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Hayashi, M.
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Lin, S. H.
;
Kim, S. K.
Conformation-dependent properties of L-tyrosine and L-tryptophan in neutral and radical cations were studied by using the density functional theory (DFT) with a new density functional M05-2X. The results are compared with those obtained by using the conventional DFT (B3LYP). Results obtained by both types of DFT were in qualitative accord, including the existence of two conformational subgroups and their subgroup-dependent adiabatic ionization energy and hydrogen bonding. On the other hand, quantitative differences were found between the two DFT methods as well: the M05-2X method successfully reproduced experimental adiabatic ionization energy, whereas the B3LYP functional consistently yielded significantly lower values by 0.2-0.3 eV. More importantly, natural bond orbital (NBO) analysis for cationic conformers showed that all conformers of L-tyrosine and L-tryptophan undergo charge localization upon ionization regardless of the presence of intramolecular hydrogen bonding, unlike the case of L-phenylalanine that was treated earlier by other studies. Different degrees of charge localization among all three aromatic amino acids are explained by employing a simple model in which the aromatic amino acid is assumed to consist of two submoieties of distinct cationic core: the backbone and aromatic side chain. The difference in adiabatic ionization energy between these two submoieties is found to govern the degree of charge localization.
Excitation properties of the H3 defect center in diamond: A theoretical study
(2009-06-16)
Lin, Chih-Kai
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Chang, Huan-Cheng
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Hayashi, M.
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Lin, S. H.
;
應用化學系
Theoretical calculations on electronic excitation energies and absorption cross sections of the H3 defect center in diamond were performed. We constructed model clusters with up to 180 atoms to imitate the local environment of the defect center and conducted first-principle calculations. TD-DFT predicted most accurately vertical excitation energy, whereas TD-HF and CIS provided rough estimations for one- and two-photon absorption cross sections. It was found that a model cluster with a diameter larger than similar to 1.0 nm is required, while relatively low-cost level of theory and basis set are sufficient for characterizing the excitation properties. (c) 2009 Elsevier B.V. All rights reserved.
Experimental and theoretical investigation of high-power laser ionization and dissociation of methane
(2007-09-27)
Sharifi, A.
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Kong, F.
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Chin, S. L.
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Mineo, H.
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Dyakov, Y.
The main purpose of this paper is to report the high-power laser ionization-dissociation of CH4 at various femtosecond (fs) laser intensities (from 1 x 10 14 W/cm(2) to 2 x 1015 W/cm(2)) with a laser pulse duration of 48 fs. The generalized molecular Keldysh theory has been applied to calculate the ionization yields for CH4+ and CH4++. Outside the influence of the A intense laser, we propose to calculate the mass spectra due to the decomposition of CH4+ and CH4++, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The agreement between the experimental mass spectra and calculated mass spectra seems to be reasonable.
Highly Multiphoton Excitation of Molecule by Intense Laser Field
(2009)
Teranishi, Y.
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Hayashi, M.
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Song, D.
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Azarm, A.
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Kong, F.
Multiphoton excitation of molecule by intense laser field is studied theoretically to explain the recent experiments of neutral fragmentation Neutral fragments are created from highly excited parent molecule Excitation mechanism is discussed with the use of Floqet theory.
Highly multiphoton molecular excitation by an intense laser pulse
(2008)
Teranishi, Y.
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Hayashi, M.
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Kong, F.
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Chin, S. L.
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Chao, S. D.
Multiphoton excitation of molecules by an intense laser field is treated. When the first excitation energy is much larger than both the photon energy and the transition energy between excited states, excited states are strongly coupled with each other by the photon, even though coupling with the ground state is weak. In such a case, a kind of collective excitation takes places, in which the excitation probability of every excited state is almost linear as functions of intensity on a log-log plot, and the slope is independent of the final state. By taking methane and formaldehyde as examples we numerically study this process.
Investigation of Conformation-Dependent Properties of L-Phenylalanine in Neutral and Radical Cations by Using a Density Functional Taking into Account Noncovalent Interactions
(2010-07-22)
Baek, K. Y.
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Hayashi, M.
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Fujimura, Y.
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Lin, S. H.
;
Kim, S. K.
Conformation-dependent properties of L-phenylalanine in neutral and radical cations have been studied by using density functional theory (DFT) with a new density functional M05-2X, which is applicable to molecular systems with nonconvalent interactions. Adiabatic and vertical ionization energies and charge distributions in the cationic conformers in addition to optimized geometrical structures for both the neutral and the cationic conformers were evaluated. These results were compared with DFT (B3LYP) results. The M05-2X results can explain the correspondence between the observed and predicted conformers without ambiguity. The possibility of conformerization of neutral conformers is indicated from the results of IRC (intrinsic reaction coordinate) profiles.
One- and two-photon absorption properties of diamond nitrogen-vacancy defect centers: A theoretical study
(2008-09-28)
Lin, Chih-Kai
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Wang, Yi-Hsieh
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Chang, Huan-Cheng
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Hayashi, M.
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Lin, S. H.
The negatively charged nitrogen-vacancy defect center, (NV)(-), in diamond has been investigated theoretically for its one-and two-photon absorption properties involving the first excited state with the (3)A(2) -> (3)E transition. Time-dependent density functional theory (TD-DFT), configuration interaction with single excitation (CIS), and complete active space self-consistent field (CASSCF) were employed in this investigation along with the 6-31G(d) basis set. Diamond lattice models containing 24-104 carbon atoms were constructed to imitate the local environment of the defect center. TD-DFT calculations in large molecular cluster models (with 85 or more carbon atoms) predicted the vertical excitation energy quite consistent with the experimental absorption maximum. CASSCF calculations were feasible only for small cluster models (less than 50 carbon atoms) but yielded one-photon absorption (OPA) and two-photon absorption (TPA) cross sections somewhat larger than the experimental values obtained with linearly polarized incident light [T.-L. Wee et al., J. Phys. Chem. A 111, 9379 (2007)]. CIS calculations in larger cluster models showed a systematic overestimation of the excitation energy while just slightly underestimated the OPA cross section and overestimated the TPA cross section. The agreements between calculations and measurements suggest that the computational approaches established in this work are applicable to explore the optical properties of related defect centers in diamond as well. (C) 2008 American Institute of Physics.
Quantum chemical calculation of intramolecular vibrational redistribution and vibrational energy transfer of water clusters
(2013-10-24)
Niu, Y. L.
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Pang, R.
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Zhu, C. Y.
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Hayashi, M.
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Fujimura, Y.
In present letter the adiabatic approximation is applied to the intramolecular vibrational redistribution (IVR) of water clusters. The isotope, blocking and cluster-size effects are investigated. This letter also examines the assumption associated with the transition state theory applied to unimolecular reactions; that is, IVR is assumed to be completed before the reaction takes place. For this purpose, we choose to study (H2O)(2)H+ -> H2O+ H3O+, and (H2O)(2) -> 2H(2)O processes. In molecular clusters, the vibrational excitation energy transfer between different normal modes has been observed. This will also be investigated for the deuterated species of (HOD)(2)H+. (C) 2013 Elsevier B.V. All rights reserved.
Quantum Chemical Modeling of Photoabsorption Properties of Two- and Three-Nitrogen Vacancy Point Defects in Diamond
(2009-06-18)
Zyubin, A. S.
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Mebel, A. M.
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Hayashi, M.
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Chang, H. C.
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Lin, S. H.
Quantum chemical calculations of the geometric and electronic structures and vertical transition energies for several low-lying excited states of the neutral and negatively charged vacancy-related point defects in diamond containing two and three nitrogen atoms (N(2)V(0), N(2)V(-), and N(3)V(0)) have been performed employing various theoretical methods (time-dependent density functional theory, equation-of-motion coupled cluster, and multireference perturbation theory) and different basis sets and using C(21)H(28), C(35)H(36), and C(51)H(52) finite model clusters. In the;round states, the vacancy-related atoms are found to be shifted away from the vacancy center by similar to 0.1 angstrom, whereas the positions of atoms from the second layer around them vacancy remain nearly unchanged, indicating a local character of geometry relaxation due to defects. The lowest excited states are formed with participation of the stretched (N(2)V) or broken (N(3)V) C-C bond and nonbonding combinations of nitrogen lone pairs as donors, with the C-C antibonding molecular orbital (MO) in N(2)V(0), broken C-C bond in N(3)V(0), and diffuse vacancy-related MOs serving as acceptors. Normally, the first excited states have a valence character, but the diffuse states are rather close in energy, especially for N(3)V(0) (2(2)A(1) and 1(2)E excited states). The first optically active excitation in the N(2)V(0) defect with the calculated energy of similar to 2.6 eV (in close agreement with the experiment) is formed by the electronic transition from the stretched C-C bond to the antibonding C-C MO, with an additional contribution from the combination of nitrogen lone pairs. For the negatively charged N(2)V(-) system, the lowest excitation to the 1(2)A(1) state is predicted to occur from the singly occupied antibonding b(1) MO to the empty diffuse a(1) orbital, but the CASPT2 calculated excitation energy, similar to 0.9 eV, underestimates the experimental zero phonon line observed at 1.26 eV. The lowest excited states of N(3)V(0), 2(2)A(1), and 1(2)E correspond to transitions from the singly occupied MO (SOMO) to the diffuse lowest vacant orbital and from the nonbonding combination of nitrogen lone pairs to SOMO, respectively, and have similar energies of about 3.1-3.3 eV, in agreement with the experimental photoabsorption band maximum at similar to 3 eV.
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
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Mebel, A. M.
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Hayashi, M.
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Chang, H. C.
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Lin, S. H.
Quantum chemical Calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV(0) and NV(-)) have been performed employing various theoretical methods and basis Sets and using finite model NC(n)H(m) clusters. Unpaired electrons in the ground doublet state of NV(0) and triplet state of NV(-) are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV(-) are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with tile first absorption band calculated at similar to 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV(0) we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (similar to 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (similar to 3.2 eV and higher). (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 119-131, 2009
Quantum Chemical Modeling of Photoadsorption Properties of the Nitrogen-Vacancy Pint Defect in Diamond
(2009-01-15)
Zyubin, A. S.
;
Mebel, A. M.
;
Hayashi, M.
;
Chang, H. C.
;
Lin, S. H.
Quantum chemical Calculations of geometric and electronic structure and vertical transition energies for several low-lying excited states of the neutral and negatively charged nitrogen-vacancy point defect in diamond (NV0 and NV-) have been performed employing various theoretical methods and basis Sets and using finite model NCnHm clusters. Unpaired electrons in the ground doublet state of NV0 and triplet state of NV- are found to be localized mainly on three carbon atoms around the vacancy and the electronic density on the nitrogen and rest of C atoms is only weakly disturbed. The lowest excited states involve different electronic distributions on molecular orbitals localized close to the vacancy and their wave functions exhibit a strong multireference character with significant contributions from diffuse functions. CASSCF calculations underestimate excitation energies for the anionic defect and overestimate those for the neutral system. The inclusion of dynamic electronic correlation at the CASPT2 level leads to a reasonable agreement (within 0.25 eV) of the calculated transition energy to the lowest excited state with experiment for both systems. Several excited states for NV- are found in the energy range of 2-3 eV, but only for the 1(3)E and 5(3)E states the excitation probabilities from the ground state are significant, with tile first absorption band calculated at similar to 1.9 eV and the second lying 0.8-1 eV higher in energy than the first one. For NV0 we predict the following order of electronic states: 1(2)E (0.0), 1(2)A(2) (similar to 2.4 eV), 2(2)E (2.7-2.8 eV), 1(2)A(1), 3(2)E (similar to 3.2 eV and higher). (C) 2008 Wiley Periodicals, Inc. J Comput Chem 30: 119-131, 2009
Theoretical study of multiphoton ionization of cyclohexadienes and unimolecular decomposition of their mono- and dications
(2008)
Zyubina, T. S.
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Mebel, A. M.
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Hayashi, M.
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Lin, S. H.
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應用化學系
Quantum chemical calculations of the geometric structure, vertical excitation energies, and ionization potentials for the isomeric pair of 1,3- and 1,4-cyclohexadienes and their mono- and dications have been performed employing a variety of theoretical methods and basis sets. The computed ionization potentials and electronic excitation energies are used to evaluate the range of internal energies available for fragmentation of the cations following multiphoton resonance ionization of the cyclohexadienes in intense laser field. The conditions governing the competition between multiple ionization and decomposition of the ions are also discussed. Calculations of stationary points on the potential energy surfaces for various fragmentation channels and relative product yields at different available internal energies are then utilized to analyze the trends in branching ratios of major dissociation products of the 1,4-cyclohexadiene(2+) dication, which include C3H3+ + C3H5+, C2H3+ + C4H5+, and C4H3+ + C2H5+.
THEORIES AND QUANTUM CHEMICAL CALCULATIONS OF LINEAR AND SUM-FREQUENCY GENERATION SPECTROSCOPIES, AND INTRAMOLECULAR VIBRATIONAL REDISTRIBUTION AND DENSITY MATRIX TREATMENT OF ULTRAFAST DYNAMICS
(2015-01-01)
Yang, L.
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Niu, Y. L.
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Lin, C. K.
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Hayashi, M.
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Zhu, C. Y.
Theory and Applications of Sum-Frequency Generations
(2014-01-01)
Lin, C. K.
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Yang, L.
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Hayashi, M.
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Zhu, C. Y.
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Fujimura, Y.
The SFG technique has become popular since the pioneering work conducted by Shen's group in late 1980s. Combined the advantages of other surface-detecting techniques, the SFG technique could identify both chemical species and orientations adsorbed on surfaces or inserted between surfaces. In view of the recent tremendous experimental activities of SFG in surface chemistry, biochemistry and material sciences, quantum chemical calculations of SFG spectra to analyze the experimental SFG spectra are badly needed. In this paper we presented the theoretical expressions of various SFG techniques and showed how to employ the quantum chemical calculations to simulate the corresponding SFG spectra.