The determination of crystal structures from powder diffraction data is a field that is rapidly expanding due to a range of computational and experimental developments. A major driving force of this expansion is the continuing development of direct space methods of structure solution. This work will show the development of the program POSSUM as a suite of direct space structure determination methods and its subsequent successful application to a number of molecular organic and inorganic materials whose crystal structures were previously unknown. Direct space methods utilise global optimisation algorithms to locate the crystal structure. This work describes the successful application of the differential evolution optimisation algorithm to structure determination from powder diffraction. Differential evolution is shown to be a robust and efficient optimisation technique with the limited number of control parameters associated with the method ensuring that optimisation of the searching is easily achieved. Investigation into improving the computer performance of the method also focused on reduction of the time taken to evaluate agreement between experimental and calculated patterns through the application of the discrete wavelet transform. This effectively reduces the number of points in the powder pattern, yet retains the same level of information as the original data set and is shown to illustrate good discrimination between solutions generated in a direct space structure solution.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:396462 |
| Date | January 2003 |
| Creators | Seaton, Colin Cormack |
| Publisher | University of Birmingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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