Date of Award

5-1975

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Physics

Supervisor

D.P. Santry

Abstract

Molecular orbital theory in general and the Complete Neglect of Differential Overlap approximation are reviewed: The Self Consistent Field perturbation theory for molecular crystals is discussed in some detail and used to study the binding energy and charge distribution of a number of real crystals which were chosen to represent a wide range of bonding situations. A discussion of intermolecular charge transfer and its possible effect on the vibrational spectra is given.

A method of obtaining the electronic band structure, and hence the density of electronic states, by a suitable transformation of the crystal orbitals obtained from the self consistent field perturbation method is presented. This transformation is used to study the band structure and density of electronic states of formamide, formic acid and urea and the band structure of naphthalene and ethylene. The effect of the crystal interactions on the molecular electronic levels is discussed.

A molecular orbital theory of the electronic states of molecular crystals is given and the resultant equations are compared to those of Davydov's valence bond approach. Some of the limitations of the neglect of differential overlap are discussed and the method is applied to the lowest singlet states of naphthalene and formamide crystals.

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