All-electron Bethe-Salpeter calculations for shallow-core x-ray absorption near-edge structures

Abstract

X-ray absorption near-edge structure spectra are calculated by fully solving the electron/core-hole Bethe-Salpeter equation (BSE) in an all-electron framework. We study transitions from shallow core states, including the Mg ${L}_{2,3}$ edge in MgO, the Li $K$ edge in the Li halides LiF, LiCl, LiBr, and LiI, as well as ${\text{Li}}_{2}\text{O}$. We illustrate the advantage of the many-body approach over a core-hole supercell calculation. Both schemes lead to strongly bound excitons, but the nonlocal treatment of the electron-hole interaction in the BSE turns out to be crucial for an agreement with experiment.