Date of Award
Brett J. Pearson
A fundamental question in molecular dynamics is the following: Given some bond-localized excitation of a molecule, what will be the pathway and rate of energy ow throughout the molecule's various degrees of freedom? This notion of vibrational energy transfer throughout a molecule is referred to as intramolecular vibrational redistribution (IVR) and has been a long-standing subject of interest in physical chemistry. Historically, IVR has been studied on a case-by-case basis. However, the essence of IVR for any molecular system is an anharmonic potential energy surface that causes dynamics in which the system's many degrees of freedom are coupled in any coordinate system. We perform a general study of anharmonic coupling by examining the dynamics resulting from the lowest-order power series potential that causes coupled motion. Specifically, we consider both quantum and classical simulations starting with a localized excitation in a single vibrational mode. We analyze the quantum case only in two dimensions, including a study of the dynamics for both wavepackets and approximate eigenstates. In the classical case, we study simulations where the initially localized energy is coupled to a large dimension bath. For a specific coupling model and system dimension, we observe energy dephasing into the bath that agrees with results from experimentally observed IVR. However, we find the unexpected result that once the size of the bath reaches a certain critical value, increasing the dimension further causes the energy in the system to remain more localized.
Liss, Kyle Lewis, "Numerical Simulations of High-Dimensional Mode-Coupling Models in Molecular Dynamics" (2016). Dickinson College Honors Theses. Paper 236.