Flux-correlation approach to characterizing reaction pathways in quantum systems: A study of condensed-phase proton-coupled electron transfer

We introduce a simple method for characterizing reactive pathways in quantum systems. Flux auto- correlation and cross-correlation functions are employed to develop a quantitative measure of dynamical coupling in quantum transition events, such as reactive tunneling and resonant energy transfer. We utilize the method to study condensed-phase proton-coupled electron transfer (PCET) reactions and to determine the relative importance of competing concerted and sequential reaction pathways. Results presented here include numerically exact quantum dynamics simulations for model condensed-phase PCET reactions. This work demonstrates the applicability of the new method for the analysis of both approximate and exact quantum dynamics simulations.