Thomas Keyes is supported by a grant from the Theoretical and Computational Chemistry Program to continue his research in the area of instantaneous normal mode (INM) analysis of liquids. Instantaneous normal modes are the harmonic modes of a representative configuration of a liquid, and they provide an intuitive description of liquid state dynamics. Keyes will further develop INM theory to treat relaxation in supercooled liquids. The self diffusion constant will be calculated from the double well modes and the distinct behavior of strong and fragile supercooled liquids will be related to the form of the double well density of states. Other properties of supercooled liquids including the Boson peak in scattering, a possible growing correlation length, stretched exponential decay of correlation functions, breakdown in the Stokes-Einstein law, and the role of spatial heterogeneity will be calculated from INM. An extension of the current theory will be investigated to introduce time-dependent adiabatic and diabatic normal mode treatments. This would extend the INM treatment to dephasing and motional narrowing. There are excellent theoretical models which explain the behavior and properties of gas phase systems where the motion is chaotic, collisions frequent, and interactions are weak. Theoretical models for the solid state are also quite well developed since periodic order in crystalline systems provides the necessary simplifications to lead to tractable solutions. The properties of liquids and supercooled liquids or glasses still present quite a challenge to theoretical interpretation. Keyes is one of several theoretical chemists who is making significant headway on developing a molecular interpretation of the physical and chemical properties of liquids. The long range impact of this work could be significant in helping to understand chemistry in condensed phases.
