New Development of Kramers-Fokker-Planck Equation of Polyatomic Molecules

如何认识凝聚态系统的动力学？我们试图从HF分子到其周围的水溶剂体系的能量弛豫过程的观点来理解它的特性，由于凝聚体系中的动力学应该在随机理论的基础上考虑，所以观测量必须进行统计计算。因此，我们建立了超多并发分子动力学模拟系统，并利用该系统对HF分子的能量弛豫过程进行了模拟，发现HF分子周围的溶剂化水分子需要其内部的振动模式进行能量传递。这种能量传递途径依赖于HF分子激发模式的振动矢量。结合Kramers-Fokker-Planck方程模型，研究了分子动力学的坐标系选择问题。我们认为，应引入与分子涨落相对应的观测量时标。结果发现，该特性适当地依赖于时间窗口的大小。

How is the dynamics in condensed system recognized? We tried to understand its characteristics from the viewpoint of energy relaxation processes from an HF molecule to its surrounding water solvent system.Since the dynamics in condensed system should be considered on the basis of stochastic theory, observables must be statistically calculated. Therefore, the super-multi concurrent molecular dynamics simulation system was developed.From those simulations of energy relaxation process using the system involved, it is found that solvated water molecules around the vibrationally excited HF molecule requires their internal vibrational modes for energy transfer. Such energy transfer pathway depends on vibrational vector of excitation mode of the HF molecule. It is concluded that intra-molecular vibrational couplings are dominant on the energy relaxation process.In relation to the Kramers-Fokker-Planck equation modeled condensed systems, furthermore, it was investigated to select which coordinates systems could represent molecular dynamics. We considered that time scales of observables should be introduced in correspondence with molecular fluctuation. It was found that the characteristics depend properly on the time window size.