Duke Jessica R, Ananth Nandini
Department of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853, United States.
J Phys Chem Lett. 2015 Nov 5;6(21):4219-23. doi: 10.1021/acs.jpclett.5b01957. Epub 2015 Oct 9.
Mapping variable ring polymer molecular dynamics (MV-RPMD) is an approximate quantum dynamics method based on imaginary-time path integrals for simulating electronically nonadiabatic photochemical processes. By employing a mapping protocol to transform from a discrete electronic state basis to continuous Cartesian phase-space variables, the method captures electronic state transitions coupled to nuclear motion using only classical MD trajectories. In this work, we extend the applicability of MV-RPMD to simulations of photoinduced excited electronic state dynamics in nonadiabatic systems with multiple avoided crossings. We achieve this by deriving a new electronic state population estimator in the phase space of electronic variables that is exact at equilibrium and numerically accurate in real time. Further, we introduce an efficient constraint protocol to initialize an MV-RPMD simulation to a particular electronic state. We numerically demonstrate the accuracy of this estimator and constraint technique in describing electronic state dynamics from an initial nonequilibrium state in six model systems, three of which describe photodissociation.
映射可变环聚合物分子动力学（MV-RPMD）是一种基于虚时路径积分的近似量子动力学方法，用于模拟电子非绝热光化学过程。通过采用一种映射协议，从离散的电子态基矢转换为连续的笛卡尔相空间变量，该方法仅使用经典分子动力学轨迹就能捕捉与核运动耦合的电子态跃迁。在这项工作中，我们将MV-RPMD的适用性扩展到具有多个避免交叉的非绝热系统中的光诱导激发电子态动力学模拟。我们通过在电子变量的相空间中推导一种新的电子态布居估计器来实现这一点，该估计器在平衡时是精确的，在实时情况下数值上也是准确的。此外，我们引入了一种有效的约束协议，将MV-RPMD模拟初始化为特定的电子态。我们通过数值方法证明了该估计器和约束技术在描述六个模型系统中从初始非平衡态开始的电子态动力学方面的准确性，其中三个模型系统描述了光解离过程。
