Theoretical Studies of Structure and Spectra of Glasses - Quantum- chemical methods at the level of ab initio Hartree-Fock Self- Consistent Field Molecular Orbital Theory will be applied to a number of problems in glass science. The basic goal will be to characterize both the short and medium range order of species in glasses by calculating values for their geometries, energetics, and spectra, and comparing with experiment. NMR spectra of various species in glasses will be calculated for several short range ordered species, e.g., boroxol rings and silicate tetrahedra in their respective glasses. Structural and spectral properties as a function of charge state and degree of polymerization will be calculated to assist in monitoring sol-gel reactions. Finally, methods will be developed to calculate polarizabilities of oxygen in various environments found in glasses and to calculate spectral energies for free and complexed probe ions used to evaluate the optical basicities of different oxidic environments in glasses. This proposal will be cofunded by DMR-Materials Theory (67%) and by CHEM-Physical Chemistry (33%). %%% It was once thought that crystalline and glassy solids were very much different structurally, with crystalls possessing both short and long range order and glasses possessing order in any meaningful sense only at the local level if at all. It now seems clear that in many cases glasses possess substantial medium range order, i.e., order on a length scale corresponding to several molecular units. Increased knowledge of the types of local and medium range order existing in glasses and the influence of such order upon the properties of the glass will make it possible to create glasses with tailored properties using nonempirical atomistic approaches. Application of quantum chemical methods to this problem is the goal of this proposal, which will be cofunded by DMR-Materials Theory (67%) and by CHEM-Physical Chemistry (33%).
