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Title: Ab initio calculations on the ground and excited states of molecules
Author: Ballard, Charles Conor
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1993
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In this work the results of highly correlated ab initio calculations on the low-lying states of propyne, furan, and the copper dimer are reported. The excitation energies obtained are used to interpret the electronic spectra of these molecules. The electronic spectra of propyne and furan have been studied using multi-reference configuration interaction techniques. For both molecules the calculations comprise the low-lying valence and s, p, and d Rydberg states, all calculations being performed at the SCF optimised geometry. A variety of basis sets were used; the inclusion of diffuse polarisation functions in the basis set is found to improve the description of the excitation processes. In contrast, the use of polarisation functions optimised for the molecular ground state has negligible effect. The electronic spectrum of propyne is interpreted on the basis of these results to be similar to that of acetylene. The computed excitation energies for the valence states of furan differ drastically from earlier theoretical results. The present results are compared to new experimental data and found to give a consistent picture for the low-lying states. The configuration interaction procedure was also utilised to determine the excitation energies of the ungerade states of Cu2 arising from the 2S+ 2D asymptote. Much of the work took the form of a preliminary investigation to investigate the feasibility of the technique and applicability of a variety of basis sets. The calculations were performed at 2.20 AA, arbitrarily, chosen to be close to the experimental equilibrium geometry. The inclusion of f-functions was found to be important in describing excitations involving states with different numbers of d electrons. Large reorganisation effects are found to accompany these excitations, which are not adequately described at the CISD level.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available