Theoretical and Computational Studies of Quantum Dynamical Processes in Condensed Matter Systems

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Gregory Voth is supported by a grant from the Theoretical and Computational Chemistry Program to continue his theoretical development of the Centroid Molecular Dynamics (CMD) technique, and to apply it to a number of important problems in the area of condensed phase dynamics of systems with quantum degrees of freedom. 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 calculation. Several applications will be investigated. Proton translocation in water and the diffusive transport of solvated and hydrated electrons will be treated. A second area of research involves the development of an initial value semiclassical dynamics approach for condensed phase systems. This approach would allow the study of both nonequilibrium and nonadiabatic processes, and treatment of nonlinear `system-bath` interactions. Finally, a formal treatment of activated quantum dynamics will be undertaken to develop a new picture of the quantum mechanical transition state. Gas phase chemical systems have been studied for a number of years, and excellent theoretical and computational techniques have been developed to model their behavior. More recently theoretical and computational methods are being developed that make it possible to treat more complex condensed phase systems. Most of the current theoretical models are classical in nature and cannot deal with the additional complications imposed by quantum effects. Voth's research addresses this additional degree of complexity and proposes the development of computational approaches designed to permit the treatment of condensed phase systems that include various quantum degrees of freedom.