Semiclassical Methods for the Evolution of Nonequilibrium Systems Undergoing Quantum Transitions

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In this project funded by the Theoretical and Computational Chemistry Program of the Chemistry Division, Herman will develop numerically efficient and accurate semiclassical methods to evaluate quantum transition probabilities and correlation functions in nonequilibrium condensed-phase, gas-phase, and molecular-beam systems. These density-evolution methods require consideration of the full quantum nature of the evolution only for times on the order of the loss of quantum phase coherence. These methods are systematically correctable and provide an estimate of the calculational error at each level of approximation. The procedures will be tested on simple model problems for which exact quantum results can be obtained and then on problems for which experimental data is available. The results of calculations using these methods will also be compared with those obtained using other computational methods.At a time when experimental methods are able to characterize increasingly fast processes, it is imperative to develop theoretical formalisms that are capable of describing such processes. The work proposed here addresses that need. It further promises to provide a framework for analyzing and interpreting ultra-fast nonequilibrium processes in excited-state systems. The planned extension of the methods to systems that are far from equilibrium will allow simulation of new classes of chemical reactions.