Photo-initiated charge-transfer processes play a central role in natural systems such as human vision and photosynthesis. While researchers have successfully modified these processes to control simple isolated systems, our understanding of photo-initiated mechanisms in realistic and complex environments is still in its infancy. In particular, recent experiments have shown that coarse-grained descriptions of solvent interactions are unable to accurately capture the electron dynamics in even relatively simple systems. These ongoing observations open an entirely new theoretical field of research in light-activated processes in explicit solvent, with the opportunity to deeply understand the real-time electron dynamics between complex interfaces.<br/><br/>To this end, we have developed a new real-time time-dependent density functional tight binding (RT-TDDFTB) approach to calculate the electron dynamics of donor-acceptor complexes with explicit solvent molecules - all treated at the quantum mechanical level. Our approach significantly differs from previous linear-response TD-DFT methods in that we directly propagate the one-electron density matrix in the presence of a non-perturbative external field. Furthermore, and most importantly, our implementation allows us to calculate the electron dynamics of large solvated systems (~10,000 atoms), whereas conventional approaches are computationally limited to only hundreds of atoms. Using this new capability, we are able to understand and rationalize electron-hole recombination effects as a function of solvent polarity and configuration. Furthermore, this new capability gives us mechanistic insight into the electron dynamics of new systems in complex environments with the goal of guiding experiments in the exploration of charge-transfer dynamics driven by time-dependent external fields.

Charge-transfer dynamics of light-harvesting systems in complex solvated environments

249th National Meeting (2015)

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