COMPUTER MODELLING OF DEFECTS IN INORGANIC MATERIALS. Robert A Jackson, Chemistry Department, Keele University, Keele, Staffs ST5 5BG, UK

The use of computer modelling methods to study defects in inorganic materials is now well-established. The methods used will be reviewed, and recent applications considered as examples. In cases where the concentration of defects is low, defects may be modelled using techniques based on Mott-Littleton methodology. This approach models point defects or defect clusters as if they are at the centre of an otherwise perfect lattice, and uses continuum methods to represent the response of more distant regions of the lattice to the presence of the defect. The approach will be illustrated by a recent study on modelling divalent impurity ions in BaLiF₃ - a system with applications in laser devices.

Higher concentrations of defects may be modelled using supercell methods, in which the defects are included as part of a large unit cell or supercell. This enables defect-defect interactions to be taken into account explicitly, and also has the advantage that all lattice properties normally calculated by lattice energy minimisation can be obtained for the defective system. The approach has been used in a study of the UO₂-PuO₂ nuclear fuel, which will be given as an example.