Theory and Simulation of Fast and Slow Dynamics in Liquids

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Thomas Keyes of Boston University is supported by the Theoretical and Computational Chemistry Program to continue his studies of liquid state dynamical theory, using a unified approach based on instantaneous a normal modes (INM), the topology of the potential energy surface, and molecular dynamics simulation. This work seeks to improve understanding of diffusion mechanisms and other slow processes in supercooled liquids, and the difference between "strong" and "fragile" liquids, with Arrhenius and stronger-than-Arrhenius temperature dependence of relaxation. Simple liquids, atomic mixtures, carbon disulfide, water, and silica will be studied, covering fragile and strong systems. A comprehensive nonequilibrium simulation/INM project will be launched on femtosecond fifth-order scattering, making contact with current experimental efforts. The outcomes of this project are expected to lead to new theoretical and simulation methods, and to physical insights into liquids based on intuitive INM/potential energy surface ideas.Supercooled liquids exist at temperatures below the ordinary freezing point to become solid. Outcomes from this work are expected to enhance the understanding of supercooled liquids, which play an important role in crystallization processes and the production of amorphous solids. As well, the research methods explored in this work have the potential to enhance theoretical research in the understanding of protein folding and structure rearrangements in clusters of molecules.