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Title: Discontinuous potential systems
Author: Bannerman, Marcus N. Campbell
ISNI:       0000 0004 2677 2199
Awarding Body: The University of Manchester
Current Institution: University of Manchester
Date of Award: 2009
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This thesis is concerned with the theory and simulation of the static and dynamic properties of discrete-potential systems. Discrete potentials are a class of models used to describe the interactions between particles in many-body systems and have applications in many fields. To investigate the dynamics of systems with discrete potentials, DYNAMO, a general event-driven molecular dynamics simulation package was developed. This software is one of the first event driven implementations to exhibit linear scaling of the computational cost. with the system size, which is the theoretically optimal scaling. DYNAMO also implements stochastic interactions, including a novel extension of DSMC proposed to attempt to include pre-collision velocity correlations, which are significant in dense or complex fluids. Using a phenomenological correction for the dynamical spatial effects, the predictions for the self diffusion coefficient of the hard sphere fluid are improved over Enskog theory at low to moderate densities. DYNAMO was used to examine a number of systems to determine their behaviour and to test theoretical predictions. Accurate simulations of large systems of hard spheres were used to test recent equations of state including a novel exponential closure of the virial series. This closure performs well in comparison to other theoretical equations of state for the fluid phase, and a revised semi-empirical equation of state is proposed for the solid phase. The collision statistics of sheared granular materials were studied to highlight the fundamental differences between elastic and inelastic systems and to critically compare Enskog theory and its approximate solutions. Overall, Enskog theory performs well; however, care must be taken with the predictions of the energy anisotropy and collision statistics. The effect of nano-colloids on the transport properties of a fluid were investigated using the binary hard sphere model. A 'fines' effect in the viscosity and a strong thermal conductivity enhancement was observed in the simulations, which are absent from the Enskog theory predictions. Finally, a simple square-well homopolymer model is examined using constant temperature molecular dynamics, coupled with replica exchange techniques. This polymer forms helical structures, and the control parameters of the model (e.g., chain stiffness, range of the attractive interactions) were completely characterised to investigate the nature and stability ofthis surprising folding behaviour. The results of all of these systems highlight the speed and versatility of both the DYNAMO simulation package and the underlying richness of discrete potential models.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available