Date of Award

9-7-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

First Advisor

Mark R. Hoffman

Abstract

Using a Lagrangian based approach, mathematical expressions were derived that analytically determine electric dipole moments, nuclear gradients, and nonadiabatic coupling coefficients for electronic states at the second-order generalized Van Vleck perturbation theory (GVVPT2) and the multireference configuration interaction (MRCI) levels of theory. The equations were expressed in a manner that ensures the slowest portions of the computer code are independent of the nuclear degrees of freedom that differentiate the energies and wavefunctions. The codes were implemented using a configuration-driven unitary group approach (UGA). Under this approach the efficient UGA method of evaluating configuration state function (CSF) matrix elements is recast within a macroconfiguration framework. The net result is a substantial increase in both the speed and flexibility of the conventional UGA procedure. Finally GVVPT2 calculations were performed to study possible interactions between the singlet and triplet states that correspond to the first two dissociation channels of the (NO)2 → 2NO reaction. Potential energy curves were determined for each electronic state and the curves were used to identify possible intermediates, transition states, and regions where nonadiabatic coupling becomes energetically favorable.

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