Browsing by Author "Nakamura, Hiroki"

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Development of semiclassical molecular dynamics simulation method
(2016-05-02)
Nakamura, Hiroki
;
Nanbu, Shinkoh
;
Teranishi, Yoshiaki
;
Ohta, Ayumi
;
應用化學系分子科學碩博班
Various quantum mechanical effects such as nonadiabatic transitions, quantum mechanical tunneling and coherence play crucial roles in a variety of chemical and biological systems. In this paper, we propose a method to incorporate tunneling effects into the molecular dynamics (MD) method, which is purely based on classical mechanics. Caustics, which define the boundary between classically allowed and forbidden regions, are detected along classical trajectories and the optimal tunneling path with minimum action is determined by starting from each appropriate caustic. The real phase associated with tunneling can also be estimated. Numerical demonstration with use of a simple collinear chemical reaction O + HCl -> OH + Cl is presented in order to help the reader to well comprehend the method proposed here. Generalization to the on-the-fly ab initio version is rather straightforward. By treating the nonadiabatic transitions at conical intersections by the Zhu-Nakamura theory, new semiclassical MD methods can be developed.
Quantum Localization of Coherent pi-Electron Angular Momentum in (P)-2,2 '-Biphenol
(2014-06-05)
Yamaki, Masahiro
;
Mineo, Hirobumi
;
Teranishi, Yoshiaki
;
Hayashi, Michitoshi
;
Fujimura, Yuichi
Controlling g-electrons with delocalized character is one of the fundamental issues in femtosecond and attosecond chemistry. Localization of pi-electron rotation by using laser pulses is expected to play an essential role in nanoscience. The pi-electron rotation created at a selected aromatic ring of a single molecule induces a local intense electromagnetic field, which is a new type of ultrafast optical control functioning. We propose a quantum localization of coherent pi-electron angular momentum in (P)-2,2'-biphenol, which is a simple, covalently linked chiral aromatic ring chain molecule. The localization considered here consists of sequential two steps: the first step is to localize the pi-electron angular momentum at a selected ring of the two benzene rings, and the other is to maintain the localization. Optimal control theory was used for obtaining the optimized electric fields of linearly polarized laser pulses to realize the localization. The optimal electric fields and the resultant coherent electronic dynamics are analyzed.
Quantum Localization of Coherent pi-Electron Angular Momentum in (P)-2,2 \'-Biphenol
(2014-06-05)
Yamaki, Masahiro
;
Mineo, Hirobumi
;
Teranishi, Yoshiaki
;
Hayashi, Michitoshi
;
Fujimura, Yuichi
Controlling g-electrons with delocalized character is one of the fundamental issues in femtosecond and attosecond chemistry. Localization of pi-electron rotation by using laser pulses is expected to play an essential role in nanoscience. The pi-electron rotation created at a selected aromatic ring of a single molecule induces a local intense electromagnetic field, which is a new type of ultrafast optical control functioning. We propose a quantum localization of coherent pi-electron angular momentum in (P)-2,2\'-biphenol, which is a simple, covalently linked chiral aromatic ring chain molecule. The localization considered here consists of sequential two steps: the first step is to localize the pi-electron angular momentum at a selected ring of the two benzene rings, and the other is to maintain the localization. Optimal control theory was used for obtaining the optimized electric fields of linearly polarized laser pulses to realize the localization. The optimal electric fields and the resultant coherent electronic dynamics are analyzed.
Semiclassical Instanton Theory of Nonadiabatic Reaction Rate Constant. I. Formulation
(2012)
Teranishi, Yoshiaki
;
Nakamura, Hiroki
;
Lin, Sheng H.
;
物理研究所
;
Institute of Physics
The reaction rate constant of electronically nonadiabatic chemical reactions is formulated by extending the semiclassical instanton theory of adiabatic chemical reaction with use of the Zhu-Nakamura theory of nonadiabatic transition. The instanton trajectory at a given temperature can be searched efficiently by the method used for multi-dimensional tunneling splitting. A compact expression of the rate constant applicable to multi-dimensional systems is derived.
The generation of stationary pi-electron rotations in chiral aromatic ring molecules possessing non-degenerate excited states
(2016-01-21)
Yamaki, Masahiro
;
Teranishi, Yoshiaki
;
Nakamura, Hiroki
;
Lin, Sheng Hsien
;
Fujimura, Yuichi
The electron angular momentum is a fundamental quantity of high-symmetry aromatic ring molecules and finds many applications in chemistry such as molecular spectroscopy. The stationary angular momentum or unidirectional rotation of pi electrons is generated by the excitation of a degenerated electronic excited state by a circularly-polarized photon. For low-symmetry aromatic ring molecules having non-degenerate states, such as chiral aromatic ring molecules, on the other hand, whether stationary angular momentum can be generated or not is uncertain and has not been clarified so far. We have found by both theoretical treatments and quantum optimal control (QOC) simulations that a stationary angular momentum can be generated even from a low-symmetry aromatic ring molecule. The generation mechanism can be explained in terms of the creation of a dressed-state, and the maximum angular momentum is generated by the dressed state with an equal contribution from the relevant two excited states in a simple three-electronic state model. The dressed state is formed by inducing selective nonresonant transitions between the ground and each excited state by two lasers with the same frequency but having different polarization directions. The selective excitation can be carried out by arranging each photon-polarization vector orthogonal to the electronic transition moment of the other transition. We have successfully analyzed the results of the QOC simulations of (P)-2,2\'-biphenol of axial chirality in terms of the analytically determined optimal laser fields. The present findings may open up new types of chemical dynamics and spectroscopy by utilizing strong stationary ring currents and current-induced magnetic fields, which are created at a local site of large compounds such as biomolecules.