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Significant progress has been made in recent years in modelling liquid crystal phases using the Monte Carlo and molecular dynamics simulation techniques. We describe the technique of molecular dynamics in the microcanonical ensemble that we have used in simulations of liquid crystal systems. A review and discussion of some of the important simulations that have been performed to date on non-spherical hard particle models, soft anisotropic single site models, and realistic atom-atom based models is presented. We report the results of molecular dynamics simulation studies of a system of particles interacting via an anisotropic potential proposed by Luckhurst and Romano, scaled by part of the well depth formulation employed by Gay and Berne. The resultant hybrid Gay-Berne Luckhurst-Romano (HGBLR) potential has an approximately spherical hard core with anisotropic long range attractive interactions with a dependency on the intermolecular vector joining a pair of sites. The spherical hard core nature of individual HGBLR centres notwithstanding we have parameterised single-site HGBLR centres to represent both calarnitic and discotic mesogens. Both systems are shown to exhibit a range of mesophases on cooling from the isotropic liquid to form a crystal, including uniaxial-nematic and columnar-like phases. Unlike previous hard particle studies these ordered phases obtain because of the presence of the long range attractive interactions. A comparison between the different structures formed with the two different parameterisations is presented including graphical representations of the simulation cell . In order to more closely represent the short range anisotropic interactions of real mesogens, a 3-HGBLR-site model has been parameterised to represent the mesogen para-terphenyl. Details of the parameterisation are discussed. Two versions of this model, a twisted central site 3-HGBLR-site site model obtained from a molecular mechanics minimum energy conformation of para-terphenyl, and an all coplanar 3-HGBLR-site site model have been studied using the molecular dynamics technique. The resultant models are found to be biaxial unlike previous anisotropic single site studies utilising soft potentials. Both models appear to exhibit a variety of uniaxial and biaxial mesophases but inclusion of the twisted site appears to promote the formation of biaxial phases. A comparison of the two models is made.

UV/visible spectrophotometry measurements, together with measurement of the temperature dependence of ac parameters G (conductance), C (capacitance) and tan (dielectric loss) for 20Hz<f<1MHz, and dc conduction, for 77K<T<300K, are performed for a number of vacuum-sublimed phthalocyanine compounds. Steady state electrical measurements and optical absorption experiments were performed on samples of sublimed heavy fraction rare-earth element, fluorochromium and lutetium bisphthalocyanine films. From the Arrhenius plot of ln(T) (where (T) is the conductivity at temperature T) it is found that two conduction regimes exist. The activation energy in the order 0.2eV at high temperatures (T > 162K) relates to the distance of singlet states below the conduction band. The low temperature activation energy indicates hopping conduction between localised states close to the Fermi level. Visible optical absorption and transmission spectra are obtained for 50nm thick sublimed films of heavy fraction rare-earth [HF(pc)(pc*)], gadolinium [Gd(pc)(pc*)] and thulium [Tm(pc)(pc*)] bisphthalocyanine compounds when they have undergone the postdeposition treatments of voltage-cycling to blue, voltage cycling to red and annealing at 393K for one hour; also for untreated fluorochromium phthalocyanine. The different post-deposition treatments produce different effects on the absorption spectra; in the case of annealing, this is attributed to the phase changes occurring in the films. The changes due to the voltage cycling are believed to be a result of oxidation processes taking place in the materials. Absorption data are also analysed in order to obtain information regarding the dispersion of refractive index and dielectric constants within optical frequency range. Absorption data are analysed in terms of a well known power law, and a value of 2.3eV is found for the optical gap E0. in HF (pc)(pc*)

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