Nonlinear spectroscopy offers a powerful tool for investigating microscopic quantum dynamics. However such quantities are often challenging to obtain theoretically for complex condensed phase systems, due to the large number of degrees of freedom.<br/><br/>For nonadiabatic systems, computationally cheap semiclassical approximations for the full electron-nuclear dynamics can be derived with the use of mapping variables. Within these approaches the electronic subsystem is mapped exactly onto a fictitious system, which has a well-defined classical limit. The dynamics associated with the mapped system is then described by an ensemble of classical trajectories. In particular, we have recently developed a new classical-trajectory mapping-based technique, called spin-PLDM, which is able to obtain the relatively short time quantum dynamics extremely accurately, does not suffer from over-damped coherences and can be applied to calculate both single and multi-time correlation functions. These characteristics make it ideally suited for obtaining optical response functions.<br/><br/>In this presentation, we will show how spin-PLDM can be applied to accurately and efficiently compute the various optical response functions that contribute to the nonlinear electronic spectra of nonadiabatic condensed phase systems, such as a Frenkel biexciton model and the Fenna-Matthews-Olsen complex. Because each optical response function is calculated independently within our approach, contributions from different dynamical pathways can be separated from the full signal, giving further insight beyond what can be achieved directly from experiment.

Electronic nonlinear spectroscopy: A novel quantum-classical approach

ACS Fall 2021

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