UC Berkeley

This thesis contributes to three areas of electronic structure theory: First, chapters 2 to 5 cover the development of energy decomposition schemes based on absolutely localized orbitals (ALMO-EDA). In chapter 2, the second-order Møller-Plesset perturbation theory (MP2) based version of this decomposition scheme is generalized to restricted and unrestricted open-shell. This new method allows to decompose the interaction energy of radical species at the MP2 level. Furthermore in chapter 3, a variational forward-backward (VFB) approach is presented to decompose the overall charge transfer (CT) stabilization energy into contributions from forward and backward donation for the density functional theory (DFT) based ALMO-EDA scheme. The two “one-way” CT states are variationally relaxed such that the associated nuclear forces can be readily obtained. In chapter 4, the DFT based ALMO-EDA scheme is extended to intermolecular interactions in the solution phase by the development of ALMO-EDA(solv); a scheme that allows the application of continuum solvent models within the framework of energy decomposition analysis.

Second, the performance of second- and third-order Møller-Plesset perturbation (MP3) theory wavefunction methods is probed for non-covalent interactions in chapter 5. The κ- regularization improves the energetics in almost all data sets for both MP2 and OOMP2. Scaled MP3 using κ-OOMP2 reference orbitals provides the most accurate results among all tested methods for non-covalent interactions across all data sets.Third in chapters 6–8, a robust computational model is presented to study mechanisms of molecular catalysts for the CO2 reduction reaction (CO2RR) to CO using DFT calculations. This model is applied and refined by the mechanistic studies of four pyridine based catalysts. In chapter 5, the bipyridine based [Fe(bpyNHEtPY2(H2O)2]2+ system is studied. In chapter 7, the mechanisms of [CoII(qpy)(H2O) ]2+ and [FeII(qpy(H2O)]2+ (with qpy = quaterpyridine) are investigated using DFT calculations to shed light on the contrasting catalytic pathways. In chapter 8, a terpyridine(tpy)-based iron polypyridine complex, [Fe(tpyPY2Me)]2+, is investigated in a combined experimental and computational approach to elucidate the different mechanisms at low and high overpotentials.