南部 伸孝

It is now confirmed that the Zhu-Nakamura (ZN) theory of nonadiabatic transition is useful to investigate various nonadiabatic chemical dynamics. The theory, being one-dimensional, presents a whole set of analytical formulas that enables us to treat the dynamics efficiently. It is also quite significant that classically forbidden transitions can be dealt with analytically. The theory can be combined with the trajectory surface hopping (TSH) method (ZN-TSH) and is demonstrated to be useful to clarify the dynamics of not only simple tri-atomic reactions but also large chemical systems. The whole set of analytical formulas directly applicable to practical systems is summarised and the applications to polyatomic systems are illustrated. Examples of polyatomic molecules are H2SO4, NH3, indolylmaleimide, cyclohexadiene (CHD), and retinal. The Fortran code for the whole set of ZN formulas is provided in Appendix for the convenience of a reader who is interested in using them. The ZN-TSH method can be combined with the QM/MM method to clarify reaction dynamics in the surrounding environment. This is named as ZN-QM/MM-TSH. The particle-mesh Ewald (PME) method can also be combined with ZN-TSH to clarify reaction dynamics in solutions. This is named as ZN-PME-TSH. Formulations of these methods are presented together with practical applications. Examples treated by ZN-QM/MMTSH are photoisomerization dynamics of retinal chromophore embedded in the protein environment. The differences in the isomerization mechanisms between rhodopsin and isorhodopsin are made clear. The faster and more efficient isomerization of rhodopsin compared to isorhodopsin is nicely reproduced. Examples of reactions in solutions are photoisomerizations of retinal and CHD. The experimentally observed long life time of the excited state of retinal is reproduced and is found to be due to the long-range solvation effect. The solvent dependent branching ratios of CHD: hexatriene (HT) are clarified for the ethanol and hexane solvents by the ZN-PME-TSH method. Both ZN-QM/MM-TSH and ZN-PME-TSH are thus demonstrated to be promising methods to deal with a wide range of nonadiabatic dynamics in large chemical and biological systems.

時間依存Schrödinger方程式やその近似式は、実時間発展により超高速現象である電子ダイナミクスを記述できる。しかし、これらの時間微分方程式を解くための時間発展の計算は、高いコストを要することが多く、これまで適用が限られていた。一方、核波束ダイナミクスの分野では、Chebyshev多項式の3項間漸化式を用いて時間発展を行う実核波束発展法が開発され、計算コストの大幅な削減に成功している。そこで本研究では、実核波束発展法を参考に、効率的な時間発展法として3項間漸化式(3TRR)法を開発した。3TRR法では、演算子変換の導入によって導かれる3項間漸化式を用いて、変換されたエネルギー・時間軸上で効率的に計算を行う。元のエネルギーと時間を得るのに必要な逆変換の式の導出も行った。3TRR法を、電子ダイナミクスを記述するRT-TDHF/TDDFT計算に適用し、計算の効率化を目指した。

A variety of chemical phenomena are governed by non-adiabatic transitions at conical intersections of potential energy surfaces, if not directly, but indirectly in the midst of the processes. In other words, the non-adiabatic transition makes one of the most significant key mechanisms in chemical dynamics. Since the basic analytical theory is now available to treat the transitions, it is possible to comprehend the dynamics of realistic chemical and biological systems with the effects of transitions taken into account properly. Another important quantum mechanical effect of tunneling can also be taken into account. Furthermore, it becomes feasible to control chemical dynamics by controlling the non-adiabatic transitions at conical intersections, and also to develop new molecular functions by using peculiar properties of non-adiabatic transitions. These may be realized, if we apply appropriately designed laser fields. This perspective review article explains the above mentioned ideas based on the authors' recent activities. The non-adiabatic chemical dynamics is expected to open a new dimension of chemistry.

UV photodissociation of OCS via 2A'((1)Delta) leads to a bimodal speed distribution of S(D-1(2)) fragment atoms whereas a single speed distribution characterizes the S atoms emerging from the 1A"((1)Sigma(.)) surface. The potential energy surfaces of these two states are almost degenerate, meaning that the bimodal state distribution observed for the 2A' state cannot be explained by the topography of the adiabatic surfaces. It is shown that the bimodal distribution originates from concomitant adiabatic and non-adiabatic dissociation processes from the 2A' state. The non-adiabatic transition is due to unlocking of an S atom electron orbital from the C-S axis by rapid rotation of CO.