Larsen Ross E, Bedard-Hearn Michael J, Schwartz Benjamin J
Department of Chemistry and Biochemistry, University of California, Los Angeles, Los Angeles, California 90095-1569, USA.
J Phys Chem B. 2006 Oct 12;110(40):20055-66. doi: 10.1021/jp0629745.
Mixed quantum/classical (MQC) molecular dynamics simulation has become the method of choice for simulating the dynamics of quantum mechanical objects that interact with condensed-phase systems. There are many MQC algorithms available, however, and in cases where nonadiabatic coupling is important, different algorithms may lead to different results. Thus, it has been difficult to reach definitive conclusions about relaxation dynamics using nonadiabatic MQC methods because one is never certain whether any given algorithm includes enough of the necessary physics. In this paper, we explore the physics underlying different nonadiabatic MQC algorithms by comparing and contrasting the excited-state relaxation dynamics of the prototypical condensed-phase MQC system, the hydrated electron, calculated using different algorithms, including: fewest-switches surface hopping, stationary-phase surface hopping, and mean-field dynamics with surface hopping. We also describe in detail how a new nonadiabatic algorithm, mean-field dynamics with stochastic decoherence (MF-SD), is to be implemented for condensed-phase problems, and we apply MF-SD to the excited-state relaxation of the hydrated electron. Our discussion emphasizes the different ways quantum decoherence is treated in each algorithm and the resulting implications for hydrated-electron relaxation dynamics. We find that for three MQC methods that use Tully's fewest-switches criterion to determine surface hopping probabilities, the excited-state lifetime of the electron is the same. Moreover, the nonequilibrium solvent response function of the excited hydrated electron is the same with all of the nonadiabatic MQC algorithms discussed here, so that all of the algorithms would produce similar agreement with experiment. Despite the identical solvent response predicted by each MQC algorithm, we find that MF-SD allows much more mixing of multiple basis states into the quantum wave function than do other methods. This leads to an excited-state lifetime that is longer with MF-SD than with any method that incorporates nonadiabatic effects with the fewest-switches surface hopping criterion.
混合量子/经典（MQC）分子动力学模拟已成为模拟与凝聚相系统相互作用的量子力学对象动力学的首选方法。然而，可用的MQC算法有很多，在非绝热耦合很重要的情况下，不同的算法可能会导致不同的结果。因此，使用非绝热MQC方法很难就弛豫动力学得出明确的结论，因为人们永远无法确定任何给定的算法是否包含了足够的必要物理过程。在本文中，我们通过比较和对比使用不同算法计算的典型凝聚相MQC系统——水合电子的激发态弛豫动力学，来探索不同非绝热MQC算法背后的物理原理，这些算法包括：最少开关表面跳跃、定相表面跳跃以及带表面跳跃的平均场动力学。我们还详细描述了一种新的非绝热算法——带随机退相干的平均场动力学（MF-SD），用于凝聚相问题的实现方式，并将MF-SD应用于水合电子的激发态弛豫。我们的讨论强调了每种算法中处理量子退相干的不同方式以及对水合电子弛豫动力学的影响。我们发现，对于三种使用塔利最少开关准则来确定表面跳跃概率的MQC方法，电子的激发态寿命是相同的。此外，激发态水合电子的非平衡溶剂响应函数与本文讨论的所有非绝热MQC算法相同，因此所有算法与实验的结果都将相似。尽管每种MQC算法预测的溶剂响应相同，但我们发现MF-SD比其他方法允许更多的多基态混合到量子波函数中。这导致MF-SD的激发态寿命比任何采用最少开关表面跳跃准则纳入非绝热效应的方法都要长。
