Theoretical investigations of the structure and properties of point defects in amorphous silicon dioxide

Many of the characteristics of electronic and optoelectronic devices can be affected dramatically the microscopic structure of the manufacturing material. An understanding of local structure and associated defects in the material is necessary to develop methods for eliminating detrimental defects and controlling beneficial ones. The present work makes use of ab initio quantum chemical methods to investigate the structure and properties of two important types of defect structures in amorphous silicon dioxide.; The present work represents the first systematic ab initio study of the nonlinear optical properties of positive charge defects in a-SiO₂. The local structure of cationic defects involving H, Li, Be, Na, and Mg has been studied and the optical properties computed in an attempt to understand the mechanism for second harmonic generation observed by Österberg and Margulis. The results show that large distortions of the oxide network are possible with large associated changes in the optical properties. The proton is shown to behave very differently from the other cationic species. A possible mechanism has been proposed based on the theoretical results and suggestions are made for future experimental work to test the hypothesis.; Paramagnetic defects have been studied using a variety of computational methods in an attempt to characterize $E\prime g$, P_b, X and Y centers. Comparisons have been made between ROHF, UHF, density functional theory, and linear response theory using both ROHF and MCSCF reference states. Differences between the results obtained using the various methods are discussed, as are the relative merits of the various theoretical approaches for future work on such systems.