Title: New theoretical approaches to simulate exciton transfer, charge separation, and proton reduction

Speaker: Dr. Pengfei (Frank) Huo, California Institute of Technology

Abstract: Understanding the real-time dynamics of solar energy harvesting and storage processes will advance the design of more efficient energy devices. However, fundamental understanding of these reactions is hindered by the complicated dynamics that not only span multiple time and length scales but also exhibit coupled dynamical hierarchies ranging from the instantaneous motion of electrons, to the strongly quantum mechanical motion of protons, and to the classical motion of the surrounding environment. Addressing these challenges demands the development of new theoretical methods which can efficiently simulate these processes with a great accuracy.

First, we start from the foundation of quantum mechanics and semi-classical dynamics to develop the partial linearized path-integral method that significantly expands the scope and reliability of condensed-phase quantum dynamics simulations. With this method we can accurately simulate exciton transfer and charge separation dynamics across multiple reaction regimes. We then apply this method to explore the coupled exciton and charge transfer dynamics in the reaction center of photosystem II.

Second, we develop and utilize quantum-embedding methods to explore the chemical reactions that require accuracy beyond the DFT level. The quantum embedding method allows local regions of a molecule to be treated with high-accuracy wavefunction methods (such as CCSD(T)), and use DFT to treat the rest majority part of the system. This method provides accuracy that is comparable to full CCSD(T) calculations on entire system, while with computational costs that is comparable to DFT calculation. We then use this method to explore the fundamental steps of electron and proton transfer reactions in cobalt-based hydrogen evolution catalysts, and demonstrate a promising design principle for efficient catalysts which generate hydrogen with a low over potential and a high turnover rate.