Localization and the Glass Transition. Brian B. Laird and Scott D. Bembenek, Department of Chemistry, University of Kansas, Lawrence, KS 66045

Disorder-induced localized excitations (tunneling modes, soft harmonic vibrations) are believed to play a dominant role in the thermodynamics and transport properties of glasses at low temperature. Using the technique of instantaneous normal-mode (INM) analysis, we explore the role that such localization plays in determining the behavior of such systems in the vicinity of the glass transition. We present evidence from computer simulations that the glass transition in two simple model systems is closely associated with a transition temperature, below which all unstable INM's become localized. This localization, analogous to the phenomenon of Anderson localization of electronic states in disordered solids, is a possible mechanism for the change in diffusion mechanism (from continuous flow to localized activated hopping) that is speculated to occur in fragile glass formers at a temperature above. In addition, recent results for localization of INM's in a model of amorphous silicon dioxide (the classic strong glass former) will be presented.