X-ray absorption spectroscopy

X-ray absorption spectroscopy (XAS) involves excitations of the core electrons into conduction bands, leaving a positive charge left in place of the excited core electron, i.e., core hole, and the excited electron, which can form a bound state called exciton. There are two approaches to modeling of XAS in VASP. The first one is based on DFT and is commonly known as the supercell core-hole (SCH) method. The second approach is based on the many-body perturbation theory and requires solving the Bethe-Salpeter equation (BSE).

Further resources

Also check out the XAS category on the VASP Wiki for a detailed documentation of the methods implemented in VASP.