In this thesis molecular dynamics (MD) simulations at a fully-atomistic level have been undertaken to study the biaxiality and the structure of the liquid crystalline phase formed by the para-heptylbenxoate diester of 2.5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP-Ph-C(_7)), which is a bent-core mesogen. This has been the first time the transition between isotropic and liquid crystalline phases has been achieved using a fully atomistic (all-atom) potential. Simulations at five different temperatures covering the nematic range of ODBP-Ph-C(_7) have been undertaken to study the temperature dependence of the biaxial ordering. Ferroelectric domains have been observed in all the systems. Simulations started from the biaxial nematic phase have been performed with the partial charges turned off to study the influence of the electrostatic interactions on the behaviour of the system. A system composed of ODBP-Ph-C(_7) and the deuterated molecule hexamethylbenzoate-d10 (HMB) has also been simulated to check the validity of the (^)2HNMR method, which is often employed to study biaxiality. MD simulations at a fully-atomistic level have been also performed for the mixture of liquid crystals E7， commercialized by Merck. The nematic phase for this mixture is grown from an isotropic phase using an fully atomistic (all-atom) potential, and in order to study the temperature dependence of the order parameter simulations at six different temperatures covering the nematic range have been performed. The internal structure of the mixture, alongside some of its material properties such as rotational viscosity and flexoelectric coefficients have been studied. Finally, ab initio calculations involving several molecular fragments which are components of some of the most common mesogens have been carried out to calculate torsional energies of key dihedral angles. Subsequently, torsional energies have been fitted using a Fourier series expansion to obtain torsional parameters for an atomistic force field. These will be used in future atomistic simulations of liquid crystals.

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The aim of this research was to investigate the feasibility of using synthetic organic polymers to control crystal growth with a view to generating organic/inorganic composites. This work was inspired by examples of biocomposites such as bone and shell. In these organic/inorganic hybrids the identity of the mineral phase and organisation of the bioorganic domains is controlled to yield functionally optimised structures. The bio-organic assemblages are multi-component systems, where pre-organised, three-dimensional scaffolds are further decorated with organic polymers which direct crystal growth at defined loci. Here the aims were (i) to investigate possible synthetic polymers that demonstrate an ability to direct crystal growth and (ii) to fabricate a three-dimensional scaffold that may be functionalised to secure control of crystal growth.

The perfection of crystals at molecular and macromolecular scales is known to impact upon the properties and utility of these materials. While the formation of defect-free crystals is desirable for various applications; the utility of crystals which evidence particular imperfections has also been recognised. Fluid-filled inclusions (macroscopic crystal imperfections) have been exten§i-vely studied as phenomena '. in geological crystals but are significantly less understood in synthetic crystals. In this study, the processes which regulate the formation of inclusions within crystals were investigated using a number of different crystallisation methods and systems, including: hexamine, adipic acid, paracetamol and potassium chloride. The impact of various experimental parameters (including: supersaturation, seeding and the impact of chemical additives) upon the formation of fluid inclusions were investigated. Fluid inclusions were found in all systems investigated. In all cases the appearance of inclusions was defined by the equilibrium morphology of the host crystal, and their distribution was related to specific crystallographic parameters. Generally, the predictive formation of fluid inclusions could be achieved by regulating the interfacial supersaturation profile of a given crystal. This observation suggested that the inherent molecular roughness of specific lattice planes and the associated growth dynamics of that surface are critical factors in the processes of inclusion formation. Seeding experiments provided an insight into the adventitious formation of inclusions by particle aggregation; analysis revealed these to be of a different type to those formed using supersaturation control. In both cases, the . retention of the crystallisation solution within the inclusions was revealed by studies with probe chemicals. Further studies revealed that a range of chemical species could be constrained within the fluid-filled volume created by inclusions and that for labile chemical species, their activity could be preserved by encapsulation within these inclusions.

Reliable prediction of molecular crystal energetics is a vital goal for computational chemistry. Currently researchers mostly rely on DFT for empirical potentials for such applications, But these methods are not systematically improvable and have a reliance on fitting to previous results. Therefore there is a need to develop new methods to perform highly accurate studies of molecular crystals using a monomer-based many-body expansion truncated at the two-body level, we present calculated energetics and optimised structures for periodic solids using high-level quantum mechanical treatments beyond density functional theory. The one- and two-body interactions are calculated using molecular quantum mechanical methods such as MP2 and we demonstrate the straightforward extension to explicitly correlated and coupled cluster theory. The higher order terms in the many-body expansion are included using a new embedding model for the crystalline environment., which takes into account electrostatics and exchange-repulsion. The environment is described using atom-centred Gaussian functions and point charges. The electrostatic potential is derived from these functions, and the exchange-repulsion contributions is derived from a density overlap scheme. The environment density is calculated self-consistently using Hartree-Fock theory. This approach is demonstrated by studying crystalline carbon dioxide, ice Xl and hydrogen fluoride. For carbon dioxide the results approach very closely those from full periodic MP2 calculations. By optimising all structural parameters in these systems we obtain lattice parameters to within 1% of experiment, as well as accurate bond lengths. For example, the calculated average 0- H bond in ice XIh is just 0,002. A from that measured experimentally. We have also studied the relative stability of two phases of ice Xl at the CCSD(T)F12 level. Ice XIh is found to be just 0.1 m Eh per formula unit more stable than the recently proposed ice Xlc phase. For hydrogen fluoride we find. that the contrasting literature reports of either the non-polar or polar phases being most stable may be a result of the two phases having similar cohesive energies and structures; optimised DF-MP2-F12/AVTZ lattice parameters for the two phases agree to within 0.05 A, and the CCSD(T)FI2/AVTZ cohesive energies indicate that the non polar phase is only O. l mE., more stable than the polar phase. Finally, the generality of the embedding method is shown by calculating the cohesive energy of lithium hydride using an embedded hierarchical approach, and we obtain excellent agreement with theoretical values in the literature and experiment.

High resolution scanning Hall probe microscopy and Hall magnetometry have been used to investigate the magnetic properties of single crystal samples of Co-doped 8r-122 and Ba-122 iron- based superconductors and high quality MgB2 thin films. We have made a quantitative analysis of the evolution of the profiles of well-isolated vortices as a function of temperature, and used a fitting procedure to extract the temperature-dependent magnetic field penetration depth, ACT). This, in turn, allowed us to infer the temperature-dependent superfluid density which has been compared with a-model results for a two band superconductor. Fit parameters yield insights into the symmetry of the order parameter at the electron and hole pockets as well as the relative contributions of the bands to the superfluid density in the iron-based crystals. Vortex imaging and 'local' magnetisation measurements, with a static Hall probe parked just above the sample surface, also yielded important information about the distribution of pinning sites, the strength of vortex pinning and the possible presence of material inhomogeneities in all samples. Finally, we have investigated vortex spatial distributions over large areas in high quality MgB2 thin films using our mK 8HPM. A careful statistical analysis of vortex positions in these films shows unusual anisotropies, with evidence of a second weak peak in the nearest neighbour vortex-vortex bond length distribution at small distances. This result was completely unexpected as one would predict such 'type 1.5 superconductivity' effects to be suppressed by strong scattering in MgB2 thin films

The thesis explores small triatomic and diatomic alkali halide molecules at state specific resolution at ultracold regime. Ab initio calculations are carried out to further publishable data to attempt a global potential energy surface for both LiF and LiCl, reacting with an approaching Li atom. Potential curve dynamics for both reactions, including well depths, avoided crossings and barrier heights are calculated to SA CASSCF and CCSD(T) level using an A VTZ basis set on all four states. This methodology is repeated as a function of the diatomic bond length. Both reactions are then compared to investigate the impact of substituting the halide. The smaller diatomic alkali halide cations are calculated up to MRCV(Q) level with basis sets ranging from A VQZ-A V6Z. Potential energy curves and dipole moments, (both permanent and transition) are calculated for the four energy states for the alkali halide series and are compared between the four molecules under examination; including LiF+, LiC\+, NaF+ and NaCl+. These curves are then fitted and inputted into LEVEL 8.0 to calculate a wealth of information including rotational and rotational constants, bound vibrational levels, Franck Condon factors and Einstein A coefficients. These findings could potentially aid in identifying the alkali halide products under Resonance Enhanced Multi Photon Ionization (REMPI).

This study has aimed to probe the morphology, interfacial structure, pre-nucleating clustering, nucleation and growth of molecular crystals at nano-scale level to establish the relationship between these processes and solid-state inter-molecular interactions. Nano-size clusters have been created, through modelling, as arrays of molecules enclosed in irregular polyhedrons with shapes corresponding to the final crystal growth morphology of the material using a developed computer program POLYPACK.

Crystallisation induced at the air-water planar interface and oil-water interface in emulsions is explored. DL-Aspartic acid crystallisation under nylon 6 spread films is studied by neutron reflectivity and ER-FTIR, and shows that the resulting crystallisation occurs within, rather than underneath the spread film layer. It is shown that 50% of the nylon 6 surface layer is composed of DL-aspartic acid, despite only 1-5% being visible to the naked eye. This is attributed to sub-visible crystalline nuclei embedded in the nylon 6 film layer, whose growth to visible dimensions is impeded by the surrounding nylon 6 film. Calcium carbonate crystallisation induced by octadecanoic acid monolayers at moderate surface pressure is studied by GDCD and ER-FTIR and shows a tilting of the monolayer hydrocarbon chain towards the surface normal as crystallization progresses. Addition of polyacrylic acid to the subphase results in formation of an amorphous calcium carbonate film under the monolayer, with no corresponding tilt of the monolayer hydrocarbon chain observed. The crystallisation of ice induced by 1-heptacosanol at the oil-in-water (o/w) interface in emulsions is studied and shows that a high curvature interface is a less effective ice nucleator than the low curvature systems. A much better ice nucleating ability is even observed when the interfacial density of 1-heptacosanol is significantly less for the low curvature systems. This is attributed to the larger critical nucleus required for crystallisation induced at a high curvature interface and a poorer ability of the I-heptacosanol to pack in a way that favours ice nucleation.Glycine crystallisation in emulsions is shown for o/w and water-in oil (w/o) cases. Crystallisation in the o/w samples using Span surfactants typically show β-phase spherical crystal aggregates, whereas the o/w show β-phase crystals with elongated morphology. Systems prepared at the phase inversion boundary typically showed a poorer nucleating ability than analogous w/o and o/w emulsion systems. The use of water-soluble additives failed to alter the glycine polymorph, but use of octanoic acid did promote a glycine crystallisation and an unusual honeycomb structure due to the aggregation of octanoic acid attracted to the glycine crystals.