Nonadiabatic kinetics in the intermediate coupling regime: comparing molecular dynamics to an energy grained master equation

TL;DR

This paper extends the energy grained master equation (EGME) to better model nonadiabatic transitions in molecular dynamics, incorporating Zhu-Nakamura theory, and validates it against ab initio simulations for a complex organic molecule.

Contribution

The paper introduces a nonadiabatic EGME approach that includes Zhu-Nakamura theory, enabling more accurate long-time dynamics modeling beyond Landau-Zener approximations.

Findings

EGME accurately captures kinetic timescales and diabatic trapping.

The approach effectively models competition between relaxation and population transfer.

Validation against ab initio dynamics shows good quantitative agreement.

Abstract

Here we outline and test an extension of the energy grained master equation (EGME) for treating nonadiabatic (NA) hopping between different potential energy surfaces, which enables us to model the competition between stepwise collisional relaxation and kinetic processes which transfer population between different potential energy surfaces of the same spin symmetry. By incorporating Zhu-Nakamura theory into the EGME, we are able to treat nonadiabatic passages beyond the simple Landau-Zener approximation, along with corresponding treatments of zero-point energy and tunnelling probability. To evaluate this NA-EGME approach, we carried out detailed studies of the UV photodynamics of the volatile organic compound C6-hydroperoxyaldehyde (C6-HPALD) using on-the-fly ab initio molecular dynamics and trajectory surface hopping. For this multi-chromophore molecule, we show that the EGME is able to quantitatively capture important aspects of the dynamics, including kinetic timescales, and diabatic trapping. Such an approach provides a promising and efficient strategy for treating the long-time dynamics of photo-excited molecules in regimes which are difficult to capture using atomistic on-the-fly molecular dynamics.