Constrained Molecular Dynamics Method Based On The New Zhu-Nakamura Formula And Its Application In Photochemical Reaction

The dissertation can be divided into two parts. One part includes the first two chapters, which mainly introduces a new nonadiabatic constrained molecular dynamics method based on a novel Zhu-Nakamura formula. The other part, namely the third chapter, introduces the application of the method in the photoisomerization of cis-stilbene.In order to understand the reaction process of molecules, molecular dynamics is a necessary tool. As the rigorous solution of the time-dependent Schrodinger equation is impossible, different assumptions are made. In the first chapter, we introduce mean-field method and trajectory surface hopping method, and then differences among Fewest Switching method, Landau-Zener method and the improved Zhu-Nakamura method are presented. Finally, some theoretical backgrounds of constrained molecular dynamics are introduced.The second chapter describes a new nonadiabatic constrained molecular dynamics. We introduce a new trajectory suface hopping method based on the improved Zhu-Nakamura formula. This method does not need to calculate nonadiabatic switching probability at each integration time step and it is very easy to evaluate the probability. Additionally, this nonadiabatic constrained molecular dynamics method to constrain internal coordinates are implemented, so that not only bond lengths but also bond angles and dihedral angles can be constrained on the dynamic process. At last, we describe how to set up the initial conditions and its programming.In the third chapter, we present the simulation testing of the photoisomerisation of stilbene based on our program and Molcas 7.5 program. In the present work, only 22 trajectories are reactive although 30 trajectories are run. The simulation results indicate that the quantum yield of trans-stilbene is 77% which is relatively large deviation from 50% by experiment, which results from only a few of trajectories are reactive. The lifetime of the first excited state is approximately 1189 fs. The reaction process is associated with two main conical intersection reported previously.