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Title: Numerical simulations of phase transitions in condensed matter
Author: Greig, David William
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1995
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The equations required to determine the motion of atoms and molecules in the molecular dynamics simulations are discussed. Atom-atom pairwise additive potentials are used to describe the van der Waals type forces between atoms and molecules. The Parrinello-Rahman description of the equations of motion of particles in a periodically repeating cell are formulated. Quaternions are used to describe the orientations of molecules. The melting transition in a two-dimensional cluster of krypton atoms is simulated. The structural changes on heating are examined in some detail and the possibility of a second-order melting transition and the existence of a hexatic phase between the solid and liquid phases is discussed. The formation of a solid from a rapidly cooled liquid-like phase is investigated. Simulations of krypton atoms in a periodically repeating cell and in a cluster are performed to examine the effects of boundary conditions. Simulations on mixtures of krypton and argon atoms, in equal proportion, in both a periodically repeating cell and in a cluster are performed. The solid structures formed are discussed in terms of glass and crystalline ordering. The orientational order-disorder transition and plastic phase in adamantane is studied. The molecular reorientation in the plastic phase is examined. Molecules occupy two possible orientations which are related by inversion. By restricting molecules to these two orientations an Ising-like model for adamantane is produced and the order-disorder phase transition is examined in a Monte Carlo simulation. Comparison of the molecular dynamics and Monte Carlo models is made. The disordered phase and reverse phase transition is discussed in terms of orientational frustration and domain formation. The suitability of using pairwise additive van der Waals type potential to represent the interaction between C60 molecules is assessed. The plastic phase of C60 is successfully modelled, however, the unit cell at low temperature predicted in the simulation is not consistent with experimental results. A discussion of other possible models of intermolecular potential is given.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available