Center for Computational Science (CCS) and Physical Chemistry Seminar 

Speaker: Xiang Sun, Assistant Professor of Chemistry at NYU Shanghai and a Global Network Assistant Professor at New York University (NYU)

Talk Title: “Theoretical Approaches to Photoinduced Charge Transfer in the Condensed Phase”

Abstract: Photoinduced charge and energy transfer in condensed-phase systems plays a crucial role in solar energy conversion, particularly in organic photovoltaic (OPV) materials. This talk will introduce newly developed computational frameworks that integrate three levels of description: rate constants, time-dependent rates, and nonadiabatic dynamics. At the core of these approaches is the linearized semiclassical (LSC) method, which enables the study of electronic transitions in complex many-body systems at an all-atom resolution. For example, we compute time-dependent charge transfer rates using nonequilibrium Fermi’s golden rule and LSC-based hierarchical approximations, culminating in the Instantaneous Marcus Theory (IMT). IMT effectively captures transient rates driven by structural relaxation and has been applied to a model OPV system: a carotenoid-porphyrin-fullerene triad dissolved in tetrahydrofuran solvent. Here, we observed a significant enhancement in transient rates caused by nonequilibrium solvent relaxation. Additionally, we introduce the multi-state harmonic (MSH) model, a method for constructing effective Hamiltonians for multi-state systems directly from all-atom data. The MSH model accounts for the heterogeneous environment’s influence on multiple electronic states by consistently treating reorganization energies across state pairs. Its nonadiabatic dynamics closely align with those obtained from full all-atom Hamiltonians, validated using various semiclassical methods. Together, these multiscale quantum dynamics methods, combining all-atom and effective Hamiltonian approaches, provide a robust and versatile framework for studying charge and energy transfer processes in complex condensed-phase systems.

Bio: Xiang Sun is an Assistant Professor of Chemistry at NYU Shanghai and a Global Network Assistant Professor at New York University (NYU). He is affiliated with the NYU-ECNU Center for Computational Chemistry at NYU Shanghai and the State Key Laboratory of Precision Spectroscopy at East China Normal University (ECNU). Before joining NYU Shanghai in 2018, he was a postdoctoral research fellow at the University of Michigan, Ann Arbor. He holds a Ph.D. in Chemistry from Brown University and a B.S. in Chemical Physics from the University of Science and Technology of China (USTC). Dr. Sun’s research focuses on developing theoretical and computational methods for studying quantum dynamics in complex condensed-phase systems, such as liquid solutions and amorphous solids, with the goal of achieving a molecular-level understanding of charge and energy transfer in solar energy conversion and its ultrafast spectroscopic signatures.  

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