White Alexander J, Gorshkov Vyacheslav N, Wang Ruixi, Tretiak Sergei, Mozyrsky Dmitry
Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
J Chem Phys. 2014 Nov 14;141(18):184101. doi: 10.1063/1.4900988.
Modeling the dynamics of photophysical and (photo)chemical reactions in extended molecular systems is a new frontier for quantum chemistry. Many dynamical phenomena, such as intersystem crossing, non-radiative relaxation, and charge and energy transfer, require a non-adiabatic description which incorporate transitions between electronic states. Additionally, these dynamics are often highly sensitive to quantum coherences and interference effects. Several methods exist to simulate non-adiabatic dynamics; however, they are typically either too expensive to be applied to large molecular systems (10's-100's of atoms), or they are based on ad hoc schemes which may include severe approximations due to inconsistencies in classical and quantum mechanics. We present, in detail, an algorithm based on Monte Carlo sampling of the semiclassical time-dependent wavefunction that involves running simple surface hopping dynamics, followed by a post-processing step which adds little cost. The method requires only a few quantities from quantum chemistry calculations, can systematically be improved, and provides excellent agreement with exact quantum mechanical results. Here we show excellent agreement with exact solutions for scattering results of standard test problems. Additionally, we find that convergence of the wavefunction is controlled by complex valued phase factors, the size of the non-adiabatic coupling region, and the choice of sampling function. These results help in determining the range of applicability of the method, and provide a starting point for further improvement.
对扩展分子系统中的光物理和（光）化学反应动力学进行建模是量子化学的一个新前沿领域。许多动力学现象，如系间窜越、非辐射弛豫以及电荷和能量转移，都需要一种包含电子态之间跃迁的非绝热描述。此外，这些动力学通常对量子相干和干涉效应高度敏感。存在几种模拟非绝热动力学的方法；然而，它们要么成本过高以至于无法应用于大型分子系统（包含数十到数百个原子），要么基于临时方案，这些方案可能由于经典力学和量子力学的不一致而包含严重的近似。我们详细介绍一种基于半经典含时波函数蒙特卡罗采样的算法，该算法涉及运行简单的表面跳跃动力学，随后是一个几乎不增加成本的后处理步骤。该方法仅需要量子化学计算中的几个量，可以系统地改进，并且与精确量子力学结果具有出色的一致性。在此，我们展示了与标准测试问题散射结果的精确解的出色一致性。此外，我们发现波函数的收敛受复值相位因子、非绝热耦合区域的大小以及采样函数的选择控制。这些结果有助于确定该方法的适用范围，并为进一步改进提供了一个起点。
