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.

中文翻译：

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从头开始多次生成的近似过程

全多重生成在理论上为激发态动力学提供了一个精确的框架，其中不同电子态的核波函数由遵循经典轨迹的一组耦合的轨迹基函数表示。轨迹基函数之间的耦合可以近似地用于处理分子系统，从而导致从头开始多重生成方法，该方法已被成功地用于研究几种分子的光化学和光物理。然而，目前在文献中缺少对其近似值及其后果的详细研究。在这项工作中，我们模拟了简单系统LiH的显式光激发和随后的激发态动力学，并且我们分析了（i）从头算起的效应在不同的观测值上产生多个产卵近似值；（ii）在逐步逼近这些近似值时，从头算起多个产卵结果趋向于数值精确的量子动力学。我们表明，尽管对于这个低维系统，从头算起多次重生所产生的近似值的粗略特征，定性激发态动力学已被充分捕获，并且可负担得起的校正可进一步应用于改善轨迹基函数之间的耦合。