Efficient Nonadiabatic Molecular Dynamics for Exploring Excitation Energy Transfer in Thermally Fluctuating Molecular Aggregates

Excitation energy transfer (EET) in molecular aggregates is a fundamental process in a wide range of condensed-phase systems, including photosynthetic complexes and organic semiconductors. Among the key factors influencing EET efficiency, thermal fluctuations play a critical role; however, accurately capturing their impact at the atomistic level remains computationally challenging. To address this, we developed an efficient simulation framework that combines the Frenkel exciton model, the nonadiabatic molecular dynamics (NAMD) simulation, and the molecular mechanics with Shepard interpolation correction (MMSIC) method. The MMSIC significantly accelerates the evaluation of excitation energies during the NAMD simulation, enabling atomistic treatment of thermal fluctuations. We applied this framework to two representative systems: exciton diffusion in crystalline anthracene and EET in the Fenna-Matthews-Olson light-harvesting complex. In both cases, the calculated results are in good agreement with previous studies, demonstrating the capability of the proposed approach to explore the interplay between thermal fluctuations and EET dynamics in complex molecular systems.