This thesis reports some quantum chemical calculations
directed at elucidating principles useful for refining calculations of electron distribution and other properties for complex molecules. In this work calculations
have been made with the valence bond and molecular
orbital methods using minimum basis sets of Slater-type orbitals on the ground states of the molecules HF and HO, and on states of HF⁺ corresponding to the ionization
of either a 1s electron or a 2pπ electron from fluorine in HF. Calculations have been made for molecular
energies, bond lengths, force constants, dipole moments, and electron distributions as given by Mulliken population analysis.
For HF, the perfect pairing model with molecule-optimized exponents yields molecular energies about 6 kcal./mole lower than the comparable molecular orbital calculations; the dipole moment calculated by the perfect
pairing method is 0.3 D. closer to the experimental
value (1.82 D.) than that calculated by the molecular
orbital method. The HF equilibrium bond length and force constants are calculated to a reasonable degree of accuracy with the two methods, although the first ionization potentials seem to be better calculated by the molecular orbital method either by Koopman's Theorem or by taking the difference between the energies of the two states.
The calculations reported in this thesis show clearly that in general free atom exponents are not reliable
for calculating molecular properties, and this is important for calculations on larger molecules which most frequently use basis functions appropriate to free atoms. As part of a programme for finding ways of optimizing
exponents relatively inexpensively, for use with more complex molecules, an approximation due to Lowdin, for overlap charge distributions in electron repulsion integrals, was tested. The results reported in this thesis show that the method has promise in providing
a way of initially optimizing exponents prior to the actual calculation wherein all integrals are evaluated
exactly. / Science, Faculty of / Chemistry, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/33636 |
| Date | January 1972 |
| Creators | Bruce, Robert Emerson |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
Page generated in 0.0017 seconds