Atomistic lattice simulation of high Tc oxides

Summary A survey is outlined of some of the normal-state crystal properties of high T_c oxides that have been calculated recently by atomistic lattice simulations.     

The coupling of intermolecular interactions to a static electric field

Using the multipole form of the long-range interaction of a pair of molecules in a static electric field, the total energy is evaluated to sixth order in the perturbation, and from this the effective pair moments and polarizabilities are derived.     

Optical,thermal and polaron energy levels in α-Al2O3

Calculations of the thermal band gap, ionisation energy and O(2p) valence band width are reported based on defect lattice methods. From these it is estimated that the large polaron is the preferred hole state in α-Al₂O₃ by about 0.4 eV. Theoretical values for the optical and thermal energy levels of Ti³⁺ in α-Al₂O₃ are also reported.     

The morphology of α-Al2O3 and α-Fe2O3: The importance of surface relaxation

Current methods for predicting crystal morphology from structure ignore the fact that real crystal surfaces are not necessarily exact terminations of the bulk structure. Instead, surfaces relax and in so doing minimise the total surface energy. This lowering of the surface energy and its influence on crystal morphology are here calculated and illustrated for α-Al₂O₃ (corundum) and α-Fe₂O₃ (haematite). The results are compared with previous studies based on Hartman-Perdok theory.     

Interatomic potentials for ionic materials from first principles calculations

Interatomic potentials for F^-…F^- and O^2-…O^2- from first principles calculations are presented and compared with previous estimates. The present non-coulombic non-polarised potential for F^2-₂ is close to that reported by Catlow and Hayns, while that for O^4-₂ is very similar to that obtained from electron-gas calculations. Electron correlation effects are found to make only a minor contribution to the short-range potentials of these systems.     

Irregularities at the {001} surface of MgO: Topography and other aspects

Non-planar sites (e.g. kinks, corners and ledges) are believed to be important in such processes as corrosion, catalysis and crystal growth, but it is difficult to obtain information about their surface relaxation or properties by experimental means. We have therefore studied them using theoretical methods, and present calculations on the topography of non-planar surface sites in the fcc materials MgO, CaO, NiO and NaCl. The models used in the calculations involved both cavities of vacancies within the planar surface and blocks of adatoms above it, and the validity of using such models is discussed. In addition, a more detailed study is undertaken for the doping of non-planar sites in MgO, and comparison is made with the bulk and at the planar {001} surface. Finally, a brief discussion of some thermal excitation energies, both in the planar surface and at selected irregularities in the non-planar surface, is given.