Application of the layer Korringa-Kohn-Rostoker method to the calculation of near-edge structure in x-ray-absorption and electron-energy-loss spectroscopy

Green’s-function methods are frequently used in the calculation of both the extended and the near-edge structures observed in x-ray-absorption and electron-energy-loss spectroscopies. To date, calculations based upon these methods have tended to be based upon a superposition of atomic potentials used to represent the crystal potential, with no attempt to calculate the self-consistent electronic potential. Many features in the near-edge region relate to charge redistribution and therefore are only approximately described by non-self-consistent electronic potentials. In this paper we show that the layer Korringa-Kohn-Rostoker method can be used in the same way as conventional Green’s-function theories for near-edge structure, with the added advantage that the self-consistent ground-state charge is used. Spectra calculated in this manner, and compared with those obtained from other Green’s-function methods, demonstrate that self-consistency is necessary to show certain features such as molecular orbital splitting in ${\mathrm{TiO}}_2$ (rutile).