William Glover, Assistant Professor of Chemistry at NYU Shanghai and Associate Director of the NYU-ECNU Center for Computational Chemistry, will deliver a seminar entitled, "Modelling excited-state processes in complex systems with new multiscale embedding methods." Hosted by Yingkai Zhang.
Zoom Link: https://nyu.zoom.us/j/95826246052
For more information about William Glover, click here.
Abstract: Photoexcited charge-transfer reactions underly numerous photophysical and photobiological processes in e.g. organic photovoltaics, the radiolysis of water, radiation damage of DNA, and photosynthesis. A common challenge to understanding these phenomena is the need to simultaneously describe multiple electronic states of both local and charge-transfer character that are strongly coupled to environment (e.g. solvent). A popular strategy is to use multiscale embedding methods such as quantum mechanics/molecular mechanics (QM/MM), wherein the system is partitioned into an active QM region containing the molecules/reaction of interest and an inactive environment with everything else that is described with computationally cheap MM forcefields. Important to the description of electronic excitations is the coupling between the QM and MM subsystems, i.e. how the QM region is embedded in the MM system. Two technical challenges arise: 1) How to partition the QM and MM regions, particularly when the solvent needs to be treated with QM, as in the case of radiolysis products of water. 2) How to capture the electronic polarization of the environment in a consistent manner for multiple electronic states, even when they cross during a photochemical reaction. I will discuss our developments in QM/MM methodology to address the above challenges. Our new methods allow us to tackle long standing questions in the fields of study of water radiolysis and photosynthesis. In particular: why do hydrated electrons, formed from the radiolysis of water, decay so quickly from their excited states to the ground state in ~50 fs? What is the origin of unidirectionality that favors charge separation in the active branch of the purple bacteria reaction center? The new tools thus open the door to accurate yet efficient simulations of photoexcited charge- transfer reactions in a plethora of complex systems.