This thesis is a study of the structure and dynamics of crystalline benzene across its solid temperature range at ambient pressure, using the techniques of molecular dynamics simulation and neutron powder diffraction. The simulations cover a wide range of properties, making comparison with the large body of experimental data that is available for benzene. A rescaling of an <i>ab initio</i> potential from the literature is proposed, and this rescaled potential is shown to give structural parameters in good accord with experiment, especially for the temperature dependence. The melting point and elastic compressibilities are determined for the model and it is found that, in the simulations, the crystal can be superheated up to the temperature of an elastic lattice instability. The implementation of a molecular dynamics program on a large array of transputers is described. The neutron powder diffraction experiment was performed primarily to study the crystal structure close to the melting point, in order to investigate reported premelting phenomena. The results contradict a previous study, but effects are seen that can be explained, using the simulations, as precursors of a form of disordering transition. The simulations predict that the full transition should be observable experimentally by the application of pressure, as this would increase the temperature range over which the solid is stable. Librational spectra are obtained from the simulations, and these indicate an explanation for some experimental results. Finally, the nature of reorientational motion about the sixfold axis of the molecule is considered. The model is shown to reproduce well the experimentally determined temperature and pressure dependence of the rate. A detailed study of the correlation of reorientation events is made, in a much greater detail than is possible experimentally. Evidence is found for only a very weak local correlation, which is a subject over which there has been considerable debate.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:645115 |
| Date | January 1990 |
| Creators | Craven, C. J. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13480 |
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