Nonadiabatic Kinetics in the Intermediate Coupling Regime: Comparing Molecular Dynamics to an Energy-Grained Master Equation

We
propose and test an extension of the energy-grained master equation
(EGME) for treating nonadiabatic (NA) hopping between different potential
energy surfaces, which enables us to model the competition between
stepwise collisional relaxation and kinetic processes which transfer
population between different electronic states of the same spin symmetry.
By incorporating Zhu–Nakamura theory into the EGME, we are
able to treat NA passages beyond the simple Landau–Zener approximation,
along with the corresponding treatments of zero-point energy and tunneling
probability. To evaluate the performance of this NA-EGME approach,
we carried out detailed studies of the UV photodynamics of the volatile
organic compound C6-hydroperoxy aldehyde (C6-HPALD) using on-the-fly ab initio molecular dynamics and trajectory
surface hopping. For this multichromophore molecule, we show that
the EGME is able to capture important aspects of the dynamics, including
kinetic timescales, and diabatic trapping. Such an approach provides
a promising and efficient strategy for treating the long-time dynamics
of photoexcited molecules in regimes which are difficult to capture
using atomistic on-the-fly molecular dynamics.

我们提出并测试了能量粗粒化主方程（energy-grained master equation, EGME）的一种扩展形式，用于处理不同势能面间的非绝热跳迁（nonadiabatic (NA) hopping），借此可对同自旋对称性的不同电子态之间布居转移的分步碰撞弛豫与动力学过程之间的竞争关系进行建模。
通过将朱-中村理论（Zhu–Nakamura theory）融入EGME，我们得以处理超越简单朗道-齐纳近似（Landau–Zener approximation）的非绝热跃迁，同时配套实现了零点能与隧穿概率的相关处理。
为评估该非绝热EGME（NA-EGME）方法的性能，我们借助随走式从头算分子动力学（on-the-fly ab initio molecular dynamics）与轨迹面跳迁（trajectory surface hopping）技术，对挥发性有机化合物C6-过氧羟基醛（C6-hydroperoxy aldehyde, C6-HPALD）的紫外光动力学开展了详尽研究。
针对这一多生色团分子，我们证明EGME能够捕捉该动力学过程的诸多关键特征，包括动力学时间尺度与diabatic俘获（diabatic trapping）。
该方法为处理光激发分子在难以通过原子级随走式从头算分子动力学捕捉的动力学区间内的长时动力学过程，提供了一种极具前景且高效的策略。