Theoretical and Computational Studies of Quantum Dynamical Processes in Condensed Matter

University Of Utah, Salt Lake City UT

Investigators

Abstract

Professor Gregory A. Voth, of the University of Utah, is supported by the Theoretical and Computational Chemistry Program to perform theoretical studies on excited-state reaction dynamics, surface chemistry and condensed-phase processes. Current focus is on extending and further developing the centroid molecular dynamics method (CMD). The CMD method is based on computing trajectories of Feynman path integral centroids using classical molecular dynamics techniques. The trajectories are then correlated and statistically weighted with the phase space Feynman path integral centroid density. The resulting time correlation function can be related by Fourier transform to the quantum time correlation function. CMD therefore allows quantum time correlation functions to be approximately calculated with a numerical effort similar to a classical MD calculations. Such methods are aimed at understanding proton transport in aqueous environments and in the simulation of hydrated electrons. Specific improvements under development include: (1) the development of a numerically exact algorithm to provide corrections to the CMD dynamics, (2) the incorporation of the semiclassical initial value representation for centroid dynamics propagation, (3) simplifying the CMD approach using Gaussian representations, including nonadiabatic dynamics of the electronic degrees of freedom, (4) inclusion of nonlinear correlation functions, and (5) inclusion of Fermi-Dirac statistics. Proton transfer in complex condensed phase systems is a fundamental aspect of many biological processes such as photosynthesis in plants and breathing in animals. The complete understanding of these processes is currently absent and in need of sophisticated theoretical treatments that are capable of accounting for the quantum-mechanical behavior of electrons and the nearly classical motion of protons. Methods developed here are well suited for dynamical descriptions associated with nearly classical proton transfer. Further understanding of these processes is requisite to the development of biomimetic materials for solar energy conversion, carbon sequestration and possibly biologically inspired environmentally friendly catalysis. Similar dynamics are of interest to atmospheric chemistry since protonated water clusters are abundant in the upper atmosphere. Research is also imparted to various communities through the training of graduate and postgraduate researchers.