Simulation of Excitation by Sunlight in Mixed Quantum-Classical Dynamics

This paper proposes a method to simulate nonadiabatic dynamics initiated by thermal light, including solar radiation, in the frame of mixed quantum-classical (MQC) methods, like surface hopping. The method is based on the Chenu-Brumer approach, which treats the thermal radiation as an ensemble of coherent pulses. It is composed of three steps, 1) sampling initial conditions from a broad blackbody spectrum, 2) propagation of the dynamics using conventional methods, and 3) ensemble averaging considering the field and realization time of the pulses. The application of MQC dynamics with pulse ensemble (MQC-PE) to a model system of nucleic acid photophysics showed the emergence of a stationary excited-state population. In another test case, modeling retinal isomerization, MQC-PE revealed that even when the underlying photophysics occurs within 200 fs, it may take tens of microseconds of continuous solar irradiation to activate a molecule photochemically. Such emergent long timescales may impact our understanding of biological and technological phenomena occurring under solar radiation.