Coarse-Grained Nonadiabatic Dynamics in Disordered Condensed Phases

The mechanisms underlying critical energy-gap fluctuations and nonadiabatic dynamics in disordered condensed phases remain elusive, and their accurate simulation poses a challenge due to the inherent complexity of these systems. In this study, we make the first attempt to leverage highly efficient coarse-grained (CG) models to investigate these fundamental mechanisms. Employing a rigorous bottom-up parameterization approach, we construct CG models for two prototypical systems: a carotenoid-porphyrin-fullerene triad in tetrahydrofuran and a perylene diimide dimer in acetonitrile. Using nonadiabatic semiclassical mapping dynamics, we evaluate a hierarchy of representations spanning fully atomistic explicit-molecule simulations, intermediate CG resolutions, and highly reduced multistate harmonic (MSH) models to assess their impact on energy-gap fluctuations and nonadiabatic properties. A distinct advantage of these explicit-molecule simulations is their ability to yield time-dependent radial distribution functions, revealing the detailed molecular picture of localized solvent rearrangement upon photoinduced charge transfer. Our results confirm that with appropriate coarse-graining of the solvent and solute, the resulting CG models faithfully preserve the structural responses, pairwise reorganization energies, and electronic population dynamics of the atomistic benchmark. Conversely, aggressive 2-heavy-atom solute mapping severely distorts local nonbonded environments. Importantly, MSH models parameterized from structurally valid CG simulations successfully reproduce explicit-molecule dynamics while discarding tens of thousands of degrees of freedom. This work provides a new, highly efficient theoretical foundation for scaling nonadiabatic dynamics simulations to larger and more complex condensed-phase systems.