Nuclear magnetic resonance (NMR) is a powerful experimental technique for probing the local environment of nuclei in materials. However, it can be difficult to separate the large number of interactions that are recorded in the resulting spectra. First-principles calculations based on quantum mechanics therefore provide much-needed support for interpreting experimental spectra. In this way, the underlying mechanisms recorded in experimental spectra can be investigated on an atomic level, and trends can be noted with which to guide the direction of future experiments. This thesis presents two cases in which first-principles calculations do just that. The first is an investigation of the perovskite structures of NaNbO<sub>3</sub>, KNbO<sub>3</sub>, LiNbO<sub>3</sub> and the related solid solutions of Na<sub>x</sub>K<sub>1-x</sub>NbO<sub>3</sub>, K<sub>x</sub>Na<sub>1-x</sub>NbO<sub>3</sub> and Li<sub>x</sub>Na<sub>1-x</sub>NbO<sub>3</sub> in order to study how structural disorder affects their NMR parameters. The second investigation involves the calculation of the Knight shift in platinum, palladium and rhodium---in their elemental bulk forms and in a set of surface structures. The Knight shift is a systematic shift in the NMR frequencies of metallic systems. It arises from the hyperfine interaction between the nuclear spins and the spins of the unpaired conduction electrons. When calculating the Knight shift, it is found that the Brillouin zone must be very finely sampled. A discussion of core polarisation is also presented. This is the polarisation of core electrons as a result of their interaction with valence electrons. In the case of Curie paramagnets, core polarisation can have a significant effect on the calculation of hyperfine parameters.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:729836 |
| Date | January 2017 |
| Creators | Lynch, Charlotte Isabella |
| Contributors | Yates, Jonathan R. ; Lynch, Charlotte Isabella |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:f44b9122-1826-410e-990d-a88dc3bb1432 |
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