REVIEW OF METHODS FOR CALCULATING NEAR-EDGE STRUCTURE

Electron energy loss inner shell near edge structures within about 30 eV of threshold can give information on charge redistribution, conduct ion band changes, coordination and structure changes on a local scale. A theoretical understanding is necessary to go beyond empirical rules based on fingerprinting. All approaches to near edge structure calcul ation in solids are derived from various band theory methods with vary ing degrees of approximation. There is a place for theories based on s imple physical ideas as well as large sophisticated calculations. In m any oxides estimates of the number of peaks and their positions can be based on an extension of single scattering EXAFS theory to include st rong second order intrashell scattering. These effects will be illustr ated in MgO and NiO. In other cases it is necessary to use band struct ure calculations to give either projected densities of states or wave functions from which matrix elements can be calculated directly. Examp les of this approach will show results of calculations for Si, diamond and SiC using the Cambridge plane wave pseudopotential code (CASTEP).