Theoretical Physical Chemistry, UR MolSYS, B6c, University of Liège, B4000 Liège, Belgium.
Department of Chemistry, Durham University, South Road, Durham DH1 3LE, United Kingdom.
J Chem Phys. 2018 Apr 7;148(13):134110. doi: 10.1063/1.5022877.
Full multiple spawning offers an in principle exact framework for excited-state dynamics, where nuclear wavefunctions in different electronic states are represented by a set of coupled trajectory basis functions that follow classical trajectories. The couplings between trajectory basis functions can be approximated to treat molecular systems, leading to the ab initio multiple spawning method which has been successfully employed to study the photochemistry and photophysics of several molecules. However, a detailed investigation of its approximations and their consequences is currently missing in the literature. In this work, we simulate the explicit photoexcitation and subsequent excited-state dynamics of a simple system, LiH, and we analyze (i) the effect of the ab initio multiple spawning approximations on different observables and (ii) the convergence of the ab initio multiple spawning results towards numerically exact quantum dynamics upon a progressive relaxation of these approximations. We show that, despite the crude character of the approximations underlying ab initio multiple spawning for this low-dimensional system, the qualitative excited-state dynamics is adequately captured, and affordable corrections can further be applied to ameliorate the coupling between trajectory basis functions.
完全多次分裂为激发态动力学提供了一个原则上精确的框架，其中不同电子态的核波函数由一组遵循经典轨迹的耦合轨迹基函数表示。通过近似处理分子系统，可以对轨迹基函数之间的耦合进行处理，从而得到从头算多次分裂方法，该方法已成功应用于研究若干分子的光化学和光物理。然而，目前文献中缺少对其近似及其后果的详细研究。在这项工作中，我们模拟了一个简单系统 LiH 的显式光激发和随后的激发态动力学，并分析了 (i) 从头算多次分裂近似对不同可观测量的影响，以及 (ii) 随着这些近似的逐步放松，从头算多次分裂结果向数值精确量子动力学的收敛性。我们表明，尽管对于这个低维系统，从头算多次分裂所基于的近似具有粗略的性质，但可以充分捕捉到定性的激发态动力学，并且可以进一步应用经济实惠的修正来改善轨迹基函数之间的耦合。
