(225i) Van Hove Correlations in Aqueous Systems: Insights from Molecular Simulation

Matthew W. Thompson^1,2, Ray Matsumoto^1,2, Peter T. Cummings^1,2

¹Multiscale Modeling and Simulation Center, Vanderbilt University, Nashville, TN, 37235-1604, USA

²Department of Chemical and Biomolecular Engineering, Vanderbilt University, Nashville, TN, 37235-1604, USA

The physical properties of water and aqueous solutions are of ubiquitous and self-evident interest to innumerable fields. Molecular simulation has for several decades informed experimental advances in describing the microscopic behavior of these molecules and how such interactions affect macroscopic properties. It is therefore of continued interest to evaluate the accuracy of different molecular simulation methods in describing these properties in exhaustive detail. Most of these properties are understood as either static structures computed via ensemble averages or transport properties computed directly or indirectly at timescales longer than the rotational relaxation time of most water models. Recent advances in neutron and X-ray scattering experiments have made it feasible to study the Van Hove correlation of water molecules and some aqueous electrolytes, which make it possible to study the time-dependent structure of these liquids at very fine resolutions, on the order of less than a picosecond in time and less than an angstrom in distance. A major limitation of these experiments, however, is that the signal produced is a statistical average over all components of a system; therefore it is difficult to understand from experiments alone which atomic interactions most strongly drive molecular behavior. Here we present results from a series of studies aimed both at better understanding these physical systems and the robustness of different force fields and molecular simulation techniques at describing them. Included are results from a broad set of force fields, encompassing classical, polarizable, reactive, and first-principles molecular dynamics simulations. Also included is an investigation of how the sizes of ions in aqueous solutions impact the very short-time and short-range correlated motions and how these observations clash with some conventional understandings of the transport properties of these solutions.

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