Theoretical Division, Center for Nonlinear Studies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Chem Phys. 2012 Feb 7;136(5):054108. doi: 10.1063/1.3680565.
Nonadiabatic molecular dynamics simulations, involving multiple Born-Oppenheimer potential energy surfaces, often require a large number of independent trajectories in order to achieve the desired convergence of the results, and simulation relies on different parameters that should be tested and compared. In addition to influencing the speed of the simulation, the chosen parameters combined with the frequently reduced number of trajectories can sometimes lead to unanticipated changes in the accuracy of the simulated dynamics. We have previously developed a nonadiabatic excited state molecular dynamics methodology employing Tully's fewest switches surface hopping algorithm. In this study, we seek to investigate the impact of the number of trajectories and the various parameters on the simulation of the photoinduced dynamics of distyrylbenzene (a small oligomer of polyphenylene vinylene) within our developed framework. Various user-defined parameters are analyzed: classical and quantum integration time steps, the value of the friction coefficient for Langevin dynamics, and the initial seed used for stochastic thermostat and hopping algorithms. Common approximations such as reduced number of nonadiabatic coupling terms and the classical path approximation are also investigated. Our analysis shows that, at least for the considered molecular system, a minimum of ~400 independent trajectories should be calculated in order to achieve statistical averaging necessary for convergence of the calculated relaxation timescales.
非绝热分子动力学模拟涉及多个 Born-Oppenheimer 势能面，通常需要大量的独立轨迹才能达到所需的结果收敛，并且模拟依赖于应该测试和比较的不同参数。除了影响模拟速度外，所选参数与轨迹数的经常减少相结合，有时会导致模拟动力学的准确性出现意外变化。我们之前开发了一种非绝热激发态分子动力学方法，采用 Tully 的最少切换表面跳跃算法。在这项研究中，我们旨在研究轨迹数和各种参数对我们开发的框架中对二苯乙烯（聚对苯乙炔的小低聚物）光致动力学模拟的影响。分析了各种用户定义的参数：经典和量子积分时间步长、朗之万动力学的摩擦系数值以及随机恒温器和跳跃算法的初始种子。还研究了常见的近似值，如减少的非绝热耦合项数和经典路径近似。我们的分析表明，至少对于所考虑的分子系统，应该计算至少~400 个独立轨迹，以实现计算弛豫时间尺度所需的统计平均收敛。
