dc.contributor.author Kong, Jing. en_US dc.date.accessioned 2014-10-21T12:38:14Z dc.date.available 2014-10-21T12:38:14Z dc.date.issued 1996 en_US dc.identifier.other AAINN15970 en_US dc.identifier.uri http://hdl.handle.net/10222/55148 dc.description Finding the conditions under which quantitatively reliable hyperfine structures can be obtained is one of the challenges of theoretical chemistry. The hyperfine structure of the $\rm\sp NH\sb2$ radical is investigated by means of multireference single and double configuration interaction techniques. Particular attention is paid to the dependence of the coupling constants on the reference space, the configuration selection energy threshold and the basis set. It has been found that the convergence can be reached at a high level of theory and excellent agreement with experiment is obtained. In order to reduce the computational cost with the minimum loss of accuracy, the basis set contraction is explored with respect to the hyperfine structure. Three popular contraction schemes are examined and it is found that all three contraction schemes yield convergence to the uncontracted one with a triple-zeta contraction, whereas the atomic natural orbital approach provides the smoothest and fastest convergence. Density functional theory calculation of isotropic couplings of the atoms B to O are also carried out with a variety of functional forms and basis sets. It is shown that the atomic isotropic coupling constants are very dependent on the functional form, the auxiliary basis set and the orbital basis set. en_US dc.description A great deal of attention has been paid experimentally and theoretically to alkaline-earth hydroxides (MOH). Previous studies have stressed the ionic bonding between the metal and the hydroxide group as a ligand. By means of high-level theoretical calculations, it is shown that another structure, HMO, exists. It has two low-lying electronic states: $\sp2\Pi$ and $\sp2\Sigma\sp+$. The studies have been carried out at several levels with a basis set of at least triple-zeta plus double polarization quality. Analysis of the electronic structures suggests that HBeO has two polarized covalent bonds formed from the sp hybrids of Be; HMgO has one covalent bond (between H and Mg) and one ionic bond and can be viewed as (HMg)$\sp+$O; HCaO has two ionic bonds represented by $\rm H\sp-Ca\sp{2+}O\sp-$. en_US dc.description The thesis concludes with a general proof that it is possible to achieve O(N$\sp2$) time scaling formally with respect to the size of the molecule (N), as opposed to O(N$\sp4$) with the conventional self-consistent-field methods. en_US dc.description Thesis (Ph.D.)--Dalhousie University (Canada), 1996. en_US dc.language eng en_US dc.publisher Dalhousie University en_US dc.publisher en_US dc.subject Chemistry, Physical. en_US dc.title Accurate predictions of molecular structures and properties. en_US dc.type text en_US dc.contributor.degree Ph.D. en_US
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