ELECTRONIC STRUCTURE STUDIES OF THE SI(100) SURFACE AND CO2 INTERACTING WITH TIO2 SURFACE CLUSTER MODELS

This thesis focuses on testing models and methods for studying the interaction between titanium dioxide and CO2, the structure of the Si(100) surface, and the effect of partial hydrogen passivation on the structure of bare dimers on the Si(100) surface.\ud Section one explores the applicability of multiple approximations to the Schrödinger equation and uses minimalistic models to determine which levels of theory and models are appropriate for capturing the structure of the surface. The Si(100) is the most important surface for semiconductor devices. It has a complex electronic structure with a small energy barrier between the ground state and two nearby local minima. Levels of theory that do not adequately include static electron correlation, find the incorrect ground state, while theories that neglect electron correlation or only include dynamic electron correlation, give an artificially high favorability to the ground state.\ud It is also important to determine what size models capture enough to the surface to replicate its correct characteristics. High order electronic structure methods necessary for capturing the physics of the surface can only be done on small models.\ud As electronic devices become smaller, an atomic level understanding is increasingly. Fabrication of electronic devices involves passivating the surface with hydrogen. The work done in this thesis uses density functional theory to explore the effect adsorbed hydrogen has on the surface structure of Si(100)\ud Increased atmospheric levels in greenhouse gases, such as CO2, are putting a continued strain on our climate. Levels of CO2 are 40% higher than they were during preindustrial times. To mitigate the effects of climate change we must make a sustained effort to limit CO2 levels in the atmosphere. Photocatalytic reduction of CO2 on TiO2 surfaces to form renewable carbon feedstocks, harnesses solar energy and reduces the consumption of fuels. To design TiO2 catalysts we need a thorough understanding of interactions between CO2 and the surface. This work uses electron structure theory to study the interaction between CO2 and cluster models of anatase and rutile titanium dioxide, to assess which methods are suitable for studying this interaction and to understand the interaction itself