Excited State Charge and Energy Transfer Mechanisms from Modern Semiclassical Theory

Charge and energy transfer reactions play a key in role in many complex chemical and biological systems. The inherently quantum mechanical nature of these processes is a significant challenge, motivating the development of new simulation methods that can incorporate quantum effects including zero-point energy, nuclear tunneling, and nonadiabatic effects at a computational cost comparable to classical molecular dynamics. This talk will introduce modern semiclassical (SC) theory as a versatile, efficient, and accurate quantum dynamics tool to discover the mechanisms of charge and energy transfer in high-dimensional systems.

The broad applicability of SC theory will be demonstrated through two key applications. The first is an atomistic investigation of the photo-isomerization and photo-fragmentation of ethylene with on-the-fly GPUaccelerated ab-initio forces. Uniquely, SC methods identify multiple reaction pathways, uncover conical intersection structures, and predict fragmentation pathways without any apriori assumptions. The second study focuses on the mechanism of vibrational de-excitation at a metal surface where nonadiabatic effects play a surprising role. Here, using only classical trajectories, SC theory captures state-to-state dynamics and identifies energy transfer mechanisms by treating nuclear and electronic motions on an even dynamical footing. The talk will conclude with a brief preview of a novel SC framework for multiscale simulations in complex systems and a discussion of future directions.