The technique of Molecular Dynamics (MD) computer simulation is coupled with the interrelated theories of light scattering and atomic polarisability to develop and test models for the Raman scattering from alkali halide systems. The primary interest is in the spectrum and intensity of the scattering from melts, but scattering from crystals is also considered. Two computationally tractable models for the Raman scattering are developed. One, a qualitative model capable of reproducing light scattering lineshapes in Nal, is based on approximations to the quantum-mechanical transition rates for the scattering processes and relies on the shell model interionic potentials from lattice dynamics to give insight into the dynamics of ionic dipole moment fluctuations, from which the scattering behaviour is extracted. The second model is a quantitative one capable of reproducing absolute scattering intensities as well as lineshapes for NaCl melts. This model is based on a detailed parameterisaton of the variation of individual ion polarisabilities with the instantaneous local ionic configuration. The model parameters are extracted from the results of electronic structure calculations on ionic systems performed elsewhere. This model has additionally been applied with some success to NaCl crystal systems. The scattering behaviour of LiF has also been considered, although no experimental comparison is available. The primary failure of the second model is its inability to predict the correct depolarisation ratio for the scattering from NaCl; reasons for this are offered. In developing the models, computer simulation techniques and the light scattering and polarisability theories are reviewed, as are aspects of alkali halide systems, especially interionic potentials suitable for use in simulations. Numerous improvements and extensions to the models are suggested.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:376897 |
| Date | January 1986 |
| Creators | Board, John Arnold |
| Publisher | University of Oxford |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://ora.ox.ac.uk/objects/uuid:948decd0-2dc0-42cd-982f-c5d9a3bad1b2 |
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