This thesis is concerned with the development of ab-initio molecular dynamics (AIMD) using density functional theory, and its application to simple diatomics and small sodium clusters. The approach follows Car and Parrinello and the local spin density (LSD) approximation is taken as a starting point for the description of the electronic states in these systems. An improvement to LSD by correcting for the spurious self-interaction terms (SIC), as proposed by Perdew and Zunger, and the way in which this can be implemented is considered. The SIC corrected LSD is tested on simple diatomic molecules, and is shown, especially for the case of H₂, to significantly improve on the LSD description of the potential energy curve and the spin pairing/unpairing transition. LSD and SIC are then compared for small sodium clusters, for which the geometries, binding energies, and polarizabilities are determined, as well as vibrational frequencies for two clusters. Conclusions are hampered by the lack of experimental data, and uncertainties due to the pseudopotential. However SIC gives a more accurate description of the binding energies, and the unique SIC orbitals allow a description of the bonding which accurately predicts the relative stabilities of the clusters and rationalises their geometries. The problems of breakdown of the Car-Parrinello (CP) method due to "nonadiabatic" effects is considered and it is shown that the problems arising during bond formation and bond breaking, as illustrated by the case of Na₂, can largely be overcome by applying an external thermostat to the fake degrees of freedom. This method is then tested using the dynamics of small sodium clusters. In particular the dynamics of the pseudorotation of Na₃ is studied and it is shown that the mechanism and information about the kinetics can be determined. Finally other methods for improving upon LSD are considered. It is shown that gradient corrections using a plane wave basis set have inherent problems in implementation. Implementation of the exact Hartree-Fock exchange is considered, and this in conjunction with a form of self-interaction correction on the correlation is shown give very accurate results for simple diatomics which are cheaper than using full configuration interaction methods.

Molecular dynamics simulation performed on modern computer workstations provides a powerful tool for the investigation of the static and dynamic characteristics of liquid crystal phases. In this thesis molecular dynamics computer simulations have been performed for two model systems. Simulations of 4,4'-di-n-pentyl-bibicyclo[2.2.2]octane demonstrate the growth of a structurally ordered phase directly from an isotropic fluid. This is the first time that this has been achieved for an atomistic model. The results demonstrate a strong coupling between orientational ordering and molecular shape, but indicate that the coupling between molecular conformational changes and molecular reorientation is relatively weak. Simulations have also been performed for a hybrid Gay-Berne/Lennard-Jones model resulting in thermodynamically stable nematic and smectic phases. Frank elastic constants have been calculated for the nematic phase formed by the hybrid model through analysis of the fluctuations of the nematic director, giving results comparable with those found experimentally. Work presented in this thesis also describes the parameterisation of the torsional potential of a fragment of a dimethyl siloxane polymer chain, disiloxane diol (HOMe(_2)Si)(_2)O, using ab initio quantum mechanical calculations.

This thesis describes the simulation of important dynamical processes involving carbon based materials. Much of the research has been aimed at examining the properties of C6o (buckminsterfullerene), the recently discovered third allotrope of carbon. Classical Molecular Dynamics (MD) simulation has been applied to study such diverse processes as fullerene film growth, the interaction of fullerenes with graphite and bare and hydrogen terminated crystal surfaces, and the implantation of atoms within C6o. We have also studied radiation damage to polymers and graphite. Collaboration with experimentalists has resulted in realistic simulations being conducted to examine physical processes. The results of simulations have been able to explain experimental results and suggest alternative methods of achieving the goals of the experiment. Several algorithms designed to improve the efficiency of simulations have been programmed and tested. Timing results for these various algorithms are presented and the most successful have been incorporated into a new MD simulation code. This has enabled systems of up to 100,000 atoms to be studied in a realistic time using single workstations (e.g. IBM RS6000 and SUN Sparc-10). The interaction of atoms is modelled by many-body potential functions. Several potential fuctions that describe covalent systems have been programmed. New · potential functions have been produced to model the long-range interactions that occur in graphite, fullelite and polymer systems, and a three-component, manybody potential has been developed for the accurate and efficient simulation of carbon-silicon-hydrogen systems. Computer visualisation and animation techniques have been applied to the interpretation and display of simulation results.

The demand for a new solvent to treat oilsands was behind the purpose of this project; molecular dynamics simulation was used in this study. Supercritical water, supercritical carbon dioxide and other selected organic solvents in their supercritical state were studied. Meso-tetraphenyl porphyrin (H2TPP) and Octaethyl porphyrin (H2OEP) are the porphyrin model compounds and, 4-Bis-(2-pyren-1-yl-ethyl)-[2, 2] bipyridinyl (PBP) is the asphaltene model compound. A solubility parameter approach was used to infer the solubility of model compounds in the supercritical fluids. First, the solubility of water, carbon dioxide, 4 selected organic solvents, and the three model compounds were computed using molecular dynamics simulation and compared with experimental results. The computed solubility parameters showed that the model compounds would dissolve in supercritical water (22.5 MPa and 645-655 K) but exhibited no solubility in supercritical carbon dioxide. / Chemical Engineering

Thesis (Ph. D.)--University of Washington, 1989. / Vita. Includes bibliographical references (leaves [210]-219).

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available in print.

Thesis (Ph.D.) in Chemistry--University of Maine, 2007. / Includes vita. Includes bibliographical references (leaves 86-90).

Thesis (Ph. D.)--Washington State University, December 2007. / Includes bibliographical references (p. 124-129).

Thesis (Ph. D.)--University of Adelaide, 1989. / Typescript (Photocopy). Includes bibliographical references (leaves vii-xiv. (second sequence)).

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.