Electronic structure studies of semiconductor surface chemistry and aluminum oxide cluster chemistry

In this dissertation, we have used electronic structure methods to study structures, spectroscopy, and chemical reactions of small molecules and materials. We have also developed new techniques to accurately model these systems. Together they provide the basis for understanding many important properties of such systems at an atomistic level.;The materials applications focus on modeling the surface chemistry of III--V compound semiconductors. Theoretical models of surface reactions have been used to learn the fundamental aspects of surface growth mechanism leading to better optimization of the growth conditions. In these studies, the surface is represented using relatively small cluster models, where the cluster boundary atoms carrying unsaturated dangling bonds may cause unphysical relaxation of the cluster geometry unless these bonds are treated carefully. We have developed pseudoatoms using parametrized effective core potentials to successfully treat these dangling bonds.;The molecular applications focus on the study of structures, photoelectron spectra, chemical bonding, chemical reactions, and materials design of neutral and anionic aluminum oxide clusters. These clusters are good model compounds to simulate the catalytic behavior of the defect sites of bulk alumina.