Development of crystallographic surfaces for modelling interactions

Abstract

This thesis addresses two separate problems - an investigation of the interaction of probe molecules with crystalline rutile and an investigation of the environment of group IA and IIA elements in organometallic compounds. Ab-initio Hartree-Fock calculations have been performed, aimed at investigating the interactions between the ionic surface of a crystal and an adsorbate molecule. Titanium dioxide, a material important for catalysis, electronic components and pigments, was chosen as the substrate, with carbon monoxide as the probe molecule. The calculations were carried out using the Crystal92 program, for the (110) surface of the Rutile polymorph of TiO(_2), employing a slab with a thickness of 5 atomic layers. The calculations investigated two orientations of the CO molecule with the molecular axis perpendicular to the surface. Results are reported showing contour diagrams for slices through the energy hypersurface parallel and perpendicular to the surface of the substrate. In order to facilitate the work described above, a program 'Builder2' was developed. This provides a convenient means for generating models of slabs of material from crystal structure data. Part of the development of Builder2 was to devise computer code to decompose standard Space Group symbols into the underlying symmetry matrices. The code for Builder2 is proprietary to Oxford Materials Ltd. and forms part of a commercial product. The environment of group IA and IIA elements in crystalline materials has not been the subject of any reported investigation. These elements, and organic ligands associated with them, play a significant role in biological systems. Around 16,000 atomic environments were extracted from the Cambridge Crystallographic Database to provide an up-to-date analysis of actual environments. The results are presented as histograms and tables, and suggestions are made for future extension of the analyses.