Semiclassical Nonadiabatic Molecular Dynamics for Molecular Exciton-Polaritons

TL;DR

This paper develops a semiclassical nonadiabatic molecular dynamics method for studying molecular exciton-polaritons, emphasizing the importance of coherence effects in their dynamics, and demonstrates its advantages over traditional surface hopping approaches.

Contribution

It introduces a new AIMC-based nonadiabatic dynamics scheme for exciton-polaritons that accurately captures coherence effects, improving upon existing mixed quantum-classical methods.

Findings

Coherence and decoherence are distinguishable during initial relaxation.

Light-matter coupling has limited impact in surface hopping simulations.

Relaxation time increases, slowing internal conversion in AIMC simulations.

Abstract

When the interaction between a molecular system and confined light modes in an optical or plasmonic cavity is strong enough to overcome the dissipative process, hybrid light-matter states (polaritons) emerge as the fundamental excitations in the system. Mixing the light and matter characters modifies molecules' photophysical and photochemical properties. It was reported that polaritonic states can be employed to control photochemical reactions, charge and energy transfer, and other processes. In addition, according to recent studies, vibrational strong coupling can be employed to enhance thermally activated chemical reactions resonantly. This work adopts a coherent state-based many-body state as the basis function to expand the light-matter Hamiltonian. The corresponding nonadiabatic Molecular Dynamics scheme is derived and implemented in the NEXMD package based on the semiclassical Ab Initio Multiple Cloning (AIMC) protocol. The scheme is demonstrated via a model system, pyridine, to demonstrate its validity. Our numerical results show that coherence and decoherence processes are distinguishable during the initial relaxation time in the AIMC simulations, while such dynamics are missing in the mixed quantum-classical surface hopping approach. Additionally, our results show that the light-matter coupling has smaller impact on the dynamics in surface hopping simulations. In the AIMC simulations, on the other hand, the relaxation time is increased, leading to a slower internal conversion and decreased equilibrium population build-up in the lowest electronically excited state. This highlights the importance of proper treatment of coherence in simulating exciton polaritons dynamics.