XAS theory

X-ray absorption near-edge spectroscopy (XANES) is a very strong (and experimentally heavily used) method for the characterization of materials. The simulation involves the excitation of a core electron into valence/conduction bands. Since for most semiconductors and insulators the electron stays strongly localized on the atom, the inclusion electron-hole interactions in the calculations is absolutely crucial. For this means two methods are mainly used:

• Super-cell core-hole (SCH) method.
• Bethe-Salpeter equation (BSE) method.