Quasi-classical approaches to vibronic spectra revisited

TL;DR

This paper revisits quasi-classical methods for vibronic spectra, proposing a generalized quantum time correlation function that enhances simulation accuracy by incorporating multiple TCFs and enabling dynamics on various potential energy surfaces.

Contribution

It introduces a generalized quantum TCF framework that unifies existing TCFs and facilitates the development of improved quasi-classical simulation protocols for vibronic spectra.

Findings

Performance varies with different TCFs on anharmonic models

Generalized TCF offers flexibility for better numerical methods

Potential for improved vibronic spectra simulations

Abstract

The framework to approach quasi-classical dynamics in the electronic ground state is well established and is based on the Kubo-transformed time correlation function (TCF), being the most classical-like quantum TCF. Here we discuss whether the choice of the Kubo-transformed TCF as a starting point for simulating vibronic spectra is as unambiguous as it is for vibrational ones. A generalized quantum TCF is proposed that contains many of the well-established TCFs as particular cases. It provides a framework to develop numerical protocols for simulating vibronic spectra via quasi-classical trajectory-based methods that allow for dynamics on many potential energy surfaces and nuclear quantum effects. The performance of the methods based on the well-known TCFs is investigated on 1D anharmonic model systems at finite temperatures. The flexibility inherent to the formulation of the generalized TCF provides a route to construct new TCFs that may lead to better numerical protocols as is shown on the same models.