Finesse in Quantum Chemistry: Accurate Energetics Relevant for Reaction Mechanisms

Citation

Carter, Emily Ann (1987) Finesse in Quantum Chemistry: Accurate Energetics Relevant for Reaction Mechanisms. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/GVJQ-6Y71. https://resolver.caltech.edu/CaltechETD:etd-11212003-111159

Abstract

A general, systematic approach for calculating accurate energetics for chemical processes within the framework of ab initio electronic structure theory is presented. The correlation-consistent configuration interaction (CCCI) method utilizes generalized valence bond wavefunctions as the starting point for the CI, which emphasizes the inclusion of only the dominant correlations dictated by the physics of the problem. The CI expansion truncates quickly, so that processes involving polyatomic molecules, which could not be addressed with conventional CI methodology, may now be treated easily.

A variety of applications of the method are presented, including the prediction of bond energies, electronic excitation energies, and energetics of chemical reactions, for both organic and transition metal-containing molecules. In cases where experimental data are available, the agreement is generally excellent (within 1-5 kcal/mol). We have used these quantitative results, along with qualitative aspects of the wavefunctions, to assess the bonding in and reactivity of a series of organic, organometallic, and inorganic molecules. These studies have produced a number of simple concepts useful for predicting the stability and reactivity of ligands attached to transition metals. Finally, key mechanistic pathways in two transition metal-catalyzed reactions have been examined using the CCCI approach: (i) the chain initiation step for the Fischer-Tropsch synthesis of hydrocarbons; and (ii) the Ag-catalyzed olefin epoxidation reaction.

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