SSAIMS-Stochastic-Selection Ab Initio Multiple Spawning for Efficient Nonadiabatic Molecular Dynamics.

Basile F E Curchod,Todd J Martínez,William J Glover

doi:10.1021/acs.jpca.0c04113

Abstract

Ab initio multiple spawning provides a powerful and accurate way of describing the excited-state dynamics of molecular systems, whose strength resides in the proper description of coherence effects during nonadiabatic processes thanks to the coupling of trajectory basis functions. However, the simultaneous propagation of a large number of trajectory basis functions can be numerically inconvenient. We propose here an elegant and simple solution to this issue, which consists of (i) detecting uncoupled groups of coupled trajectory basis functions and (ii) selecting stochastically one of these groups to continue the ab initio multiple spawning dynamics. We show that this procedure can reproduce the results of full ab initio multiple spawning dynamics in cases where the uncoupled groups of trajectory basis functions stay uncoupled throughout the dynamics (which is often the case in high-dimensional problems). We present and discuss the aforementioned idea in detail and provide simple numerical applications on indole, ethylene, and protonated formaldimine, highlighting the potential of stochastic-selection ab initio multiple spawning.

Highlights

Developing accurate and efficient nonadiabatic ab initio molecular dynamics methods is an important challenge for theoretical chemistry
We propose a variation of the ab initio multiple spawning (AIMS) method, called stochastic-selection AIMS (SSAIMS), which exploits the decoupling between trajectory basis functions (TBFs) that occurs naturally in the course of the dynamics to reduce the number of running trajectories
We start by discussing the difference between an AIMS and an ESSAIMS run for the excited-state dynamics of a medium-size molecule, indole

Summary

Introduction

Developing accurate and efficient nonadiabatic ab initio molecular dynamics methods is an important challenge for theoretical chemistry. The description of nonadiabatic phenomena requires nuclear dynamics beyond the Born−Oppenheimer approximation and, quite often, beyond the standard classical approximation for the nuclei. The nuclear dynamics relies on accurate and efficient electronic structure calculations for potential energy surfaces, their gradients, and derivatives of the electronic wave functions (which lead to the nonadiabatic coupling matrix elements that govern the propensity for transitions between electronic states). We focus primarily on the first problem, i.e. the efficient and accurate description of nonadiabatic dynamics. The required potential energy surfaces and couplings might come from parametrized analytic functions or “on the fly” ab initio quantum chemical methods, we will generally prefer the latter

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