Abstracts Category : Other

Gap Engineering and Simulation of Advanced Materials

by Kiran Prasai

Generating computer models of materials thatfaithfully represent <i>all</i> of our current state ofknowledge about those materials has remained an unsolved problem.In particular, models of amorphous solids following from amolecular dynamics (MD) simulation commonly show structural defectsand related mid-gap electronic states that are not present in thereal materials. In this dissertation, we present a novel way ofusing <i>a priori</i> knowledge of the electronic bandgap of amorphous systems to guide MD simulations. This involvescomputing Hellmann-Feynman forces associated with certainelectronic states and judiciously coupling them to the total forcein MD simulations. We show that such a method can provide a meansto purge structural defects. By producing a series of models ofamorphous carbon with varying<i>sp2/sp3</i>ratio, well show that this method offers useful new flexibility inmodeling. And, we demonstrate, for the first time, how MDsimulations can be biased to systematically model aninsulator-metal transition in glassy systems. The nature ofelectron transport in eSe3Ag glass isexplored using advanced methods and important inferences are drawnabout the role of Ag atoms in electronic conductivity. Inparticular, it is shown that a certain Se-Ag phase in this glassplays a dominant role in electron transport. We also investigatethe response of <i>a-</i>GeSe3Agto radiation damage using empirical interatomic interactions andshow that the glass exhibits rapid recovery after a knock on event.Finally, we consider the the coupling between lattice vibrationsand electronic states in disordered systems and show that disorderinduced localization of states dictates the thermal modulation ofelectronic energy.Advisors/Committee Members: Drabold, David A. (Advisor).