Off-campus UNL users: To download campus access dissertations, please use the following link to log into our proxy server with your NU ID and password. When you are done browsing please remember to return to this page and log out.
Non-UNL users: Please talk to your librarian about requesting this dissertation through interlibrary loan.
CONTRIBUTIONS TO ATOMIC AND MOLECULAR INTERACTIONS (VALENCE BOND, BASIS SET SUPERPOSITION ERROR)
Abstract
This dissertation examines several molecular systems by the ab initio multiconfigurational valence bond (MCVB) method. Four major topics are addressed: (1) contributions to intermolecular forces, (2) the nature of basis set superposition error (BSSE) and a comparison of two methods to estimate its magnitude, (3) the photoelectron spectrum of cyclopropane and its relationship to recent mass spectral experiments, (4) a generalized superposition of resonance structures (GSRS) method for ranking the importance of different resonance structures in conjugated pi systems in model molecules. The interaction energies of He(,2) and Be(,n) were calculated and partitioned into dispersion, induction, charge transfer, and electrostatic plus Pauli repulsion components. The general conclusions drawn from these studies suggest that charge transfer effects may be smaller than previously thought. The estimation of BSSE is examined by using both full functional and virtual counterpoise methods. The results of each method are compared to "frozen core" calculations. It was found that the full counterpoise method overcorrects in some cases whereas the virtual did not. The first two electronic states of the cyclopropane radical cation were calculated and the potential energy surface for each characterized. The origin of the double hump in the first peak in the photoelectron spectrum is explained and the energy surfaces are used to rationalize observations from mass spectral studies such as the randomization of the three carbon atoms upon ionization and the propene-like behavior upon increasing internal energy of the radical cation. The theoretical basis for traditional resonance theory of organic molecules is investigated by calculating the separate contributions of resonance structures to the total energy of the pi system of several model systems within an ab initio framework. Six molecules were calculated benzene, fulvene, 3,4-dimethylenecyclobutene, and trimethylenecyclopropane, butadiene, and hexatriene. The results suggest that the traditional Kekule structures are indeed the most important, with respect to energy, in this model.
Subject Area
Chemistry
Recommended Citation
COLLINS, JACKIE RAY, "CONTRIBUTIONS TO ATOMIC AND MOLECULAR INTERACTIONS (VALENCE BOND, BASIS SET SUPERPOSITION ERROR)" (1986). ETD collection for University of Nebraska-Lincoln. AAI8624583.
https://digitalcommons.unl.edu/dissertations/AAI8624583