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Title: The use of periodic ab initio methods in the determination of NMR quadrupole parameters
Author: Johnson, Clive
ISNI:       0000 0001 3591 0619
Awarding Body: Open University
Current Institution: Open University
Date of Award: 2003
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Although significant progress has been made in recent years in the development of new experimental techniques for the measurement of high-resolution nuclear magnetic resonance spectra for half-integer quadrupolar nuclei in solids, a particular problem still arises in the assignment of these resonances for materials in which there are several distinct crystallographic sites. This thesis demonstrates that a periodic Hartree-Fock ab initio method, based on modified 3-21G and 6-21G elemental basis sets used in a consistent manner, enables linear correlations between calculated and experimental NMR quadrupoie parameters to be obtained. Comparable calculations using density functional theory did not significantly improve the correlations. In the case of 23Na NMR experiments, the correlations are of sufficient accuracy to confirm and provide new assignments for a range of crystalline sodium compounds, including Na2SO3, Na2HP04, Na4P2O7 and Na5P3O10 6H2O. Furthermore, it is demonstrated that the calculations are sufficiently sensitive to the local electronic environment such that (i) anomalies in crystal structure determinations for Na4P2O7 and the phase I polymorph of anhydrous Na5P3O10 can be identified and (ii) information can be gained on the position of hydrogen within the hydrogen bond in Na2HPO4. Specific calculations for the ionic compound sodium oxide chloride, Na3OCl, provide insight into the origin of the Stemheimer factor and its link to the polarization of the sodium 2p orbitals. The periodic ab initio correlation method is also applied to 17O NMR studies and is shown to be independent of the nature of the oxygen bonding. Specific calculations, using pseudopotentials for silicon, are made for the 10 distinct oxygen sites in fenierite, a siliceous zeolite. It is shown that the calculations are able to distinguish between two proposed crystal structures for this material. A summary of results for 27Al and 51V is also presented.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Crystal code