Theoretical Studies of Glasses

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0081006DraboldThis grant supports the work of a mid-career PI, interested in a theoretical study of the electronic properties of chalcogenide glasses. These are glasses, which involve selenium and sulfur, in their pure form and also alloys involving them. There are three research projects: In the first one, there is a calculation of the electron states near the optical gap, including lattice dynamics effects and using state of the art methods. These states are of critical importance in the transport, doping and optical characteristics of these materials. The second project studies light induced structural changes. Experiments show that such light induced structural changes may be spatially non-local and lead to dramatic phenomena such as athermal photo-melting and giant photo-expansion. There will be a study of models of these glasses, using the activation-relaxation technique of Mousseau and Barkema, in conjunction with fast, approximate ab initio methods. A limited study of the surface states of selected glasses will be performed, both for their fundamental interest as well as for light-induced structural changes, especially photomelting. Finally, there are the associated methodological aspects, e. g. non-adiabatic dynamics. These studies will involve a judicious application of techniques ranging from the simplest empirical potentials to density functional methods in the local spin density approximations with generalized gradient corrections.%%%This grant supports the work of a mid-career PI who is intrigued by the photomechanical effects in chalcogenide glasses. The subject is key to an understanding of the solar cells' operating efficiency in that if their are substantial structural changes in the material, as a result of its operation as a photoelectric device, then an understanding of how that happens might suggest ways of improving the battery lifetimes. Additionally the subject is of fundamental importance since the physics involved is subtle and the effects have been beyond the reach of conventional methods and approximations.***