ab initio Quantum Chemical Analysis of Small Molecular Systems: Pushing and Expanding the Limits of Computational Capability

The Bismuth tetramer cluster (Bi4) is studied using high level ab initio techniques. Dissociation and at- omization energies are determined and visual analysis is performed on natural bonding orbitals (NBO). Substituted variants of ortho-benzyne are studied using density functional theory (DFT). The impact of differing sustituents on the triple-bond is elucidated via the analysis of several properties, as well as NBO analysis. A prototype of hydrocarbon combustion in i-propyl + O2 is analyzed using high level ab initio techniques. Relevant stationary points are studied and categorized into reaction pathways and rich potential energy surface dynamics are elucidated. A novel approach for computing harmonic vibrational frequencies is formulated, the Concordant Mode Approach (CMA). Computing diagonal force constants under this approach yields a powerful approximation that scales linearly with respect to single point energy displace- ments as opposed to the quadratic scaling of standard finite difference computations of harmonic vibrational frequencies.