Semiclassical Molecular Dynamics in Extended Systems

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V. Ara Apkarian is suported by a grant from the Theoretical and Computational Chemistry Program to perform semiclassical molecular dynamics simulations of quantum dynamic effects in extended systems. This approach has already been developed and employed successfully for gas-phase spectroscopy. The methodology is now being applied to the spectroscopy of cryogenic solids, condensed hydrogen, and hydrogen-bonded networks, as well as room-temperature liquid resonance-Raman and photon-echo spectroscopies. Quantum effects are simulated with a `black box` dependent only on inputted potential energy parameters. Due to the many degrees of freedom in these applications, the computations are very intensive. This is partially remedied by relying on short-time propagation with wavefunction reconstruction through repeated Monte Carlo sampling. In order to understand quantum dynamics in systems of large dimensionality, such as liquids and solids, new simulation methods are needed. In condensed phase spectroscopy in particular, connecting observables to the underlying molecular structures and their motions currently relies on approximate techniques. Theoretical developments that aim toward a microscopic understanding of condensed phase spectra are invaluable tools in the interpretation and design of experiments.