Hopping Around: Development of Methods for the Simulation of Non-Adiabatic Dynamics in Large Molecular Systems

Abstract

Non-adiabatic molecular dynamics methods have been developed for the calculation of charge carrier dynamics, with a focus on large molecular and materials systems. These methods move beyond the Born-Oppenheimer approximation to account for transitions between electronic states. They are powerful companions to experimental measurements in elucidating chemical phenomena. In this dissertation we first give an overview of two of the most popular methods for non-adiabatic molecular dynamics: Ehrenfest dynamics and fewest switches surface hopping (FSSH). This is followed by a description of our implementation of FSSH within a single determinant framework. We showcase our implementation by examining the relaxation dynamics in both a transition-metal-doped, semiconductor quantum dot and a set of monomer units of conjugated polymers that serve as the electron donor phase of organic solar cells. We conclude with our development of a novel non-adiabatic molecular dynamics method, surface hopping with Ehrenfest excited potential (SHEEP). SHEEP was inspired by the electronic structure of systems like our semiconductor examples and is a combination of the non-adiabatic methods described in the opening chapter. It has performed well on a series of model problems, and it has the potential for significant computational savings over the FSSH method.