We discuss existing free energy methods for use with investigation of solid-solid polymorphism. An alternative implementation for phase switch Monte Carlo is introduced which samples from two synchronised Markov chains exploring both polymorphs, using a set of generalised coordinates to transform between Markov chains. This is validated against the existing results for face-centred cubic (fcc) and hexagonal close-packed (hcp) hard sphere crystals. The extension to more complex crystals including flexibility and constraints is explored. This extension is applied to a hard sphere model of linear alkanes. A phase transition in density is accurately located between two polymorphs of n-butane with increasing density; this is suggested as a rigorous benchmark for free energy methods. We also demonstrate the importance of including anisotropic volume moves when simulating crystalline solids. Generalised coordinates for any fully flexible molecular system of soft particles are presented. These are used to investigate a coarse-grain model of cholesterol in regards to the polymorphic transition between two anhydrous cholesterol crystals. A phase transition in temperature is found and the limitations in the model are discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:640946 |
| Date | January 2014 |
| Creators | Bridgwater, Sally |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/66466/ |
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