Advanced electronic structure methods on high performance computers have been used to study new materials for technology applications and for atmospheric chemical processes of the halogens. Chapter 2 is focused on the thermodynamics of halogen oxides relevant to stratospheric ozone depletion chemistry. We calculated the thermodynamic properties of various key species to better understand what is happening in the atmosphere to help minimize our impact on the environment. This research is particularly important because of the lack of experimental data on these species. Chapter 3 is focused on the design of flexible catalysts for single electron transfer reactions using neutral Group 6B (Cr, Mo, W) pentacarbonyl complexes M(CO)5-L. It was found that various P-ligands such as phosphines, phosphalkenes, and phospha-quinomethanes can form radical cations and anions under redox conditions and that the radical site can be localized either on the metal or on the "non-innocent" ligand. More polar solutions will drive single electron transfer reactions to form the cationic and anionic metal based complexes with the appropriate oxidizing and reducing agents. Chapter 4 is the study of chemical hydrogen storage systems with a focus on borane amines. The goal was to develop economically viable and energy efficient processes to regenerate spent fuel formed by the release of hydrogen from ammonia borane. The thermodynamics for fuel regeneration processes of spent ammonia borane fuel, modeled as polyborazylene, were accurately predicted. A method using a modified Pictet-Trouton rule and calculated boiling points was used to estimate heats of formation of liquids for the prediction of the thermodynamics of reactions in the liquid phase. An effective tin catalyst with the potential to lower the cost for ammonia borane regeneration at an industrial scale was designed in collaboration with Los Alamos National Laboratory. However, it was found that at an industrial scale the process was limited due to the cost of transporting the tin catalyst around the spent fuel regeneration plant. Therefore, it was necessary to find a new method for regenerating spent ammonia borane fuel, and hydrazine was found to work very effectively in a one pot approach.