Theoretical and experimental study of the graphite 1s x-ray absorption edges

Theoretical calculations in combination with experiments for the ${\mathrm{\pi }}^{\mathrm{*}}$ and ${\mathrm{\sigma }}^{\mathrm{*}}$ x-ray absorption edges are reported for graphite. Theory and experiment agree well for the leading ${\mathrm{\pi }}^{\mathrm{*}}$ and ${\mathrm{\sigma }}^{\mathrm{*}}$ resonances. By comparing theoretical calculations for a single graphene layer that include the effect of the core hole to similar calculations that do not, we find that 1s x-ray absorption in graphite is to be associated with an excitonic effect. Both the ${\mathrm{\pi }}^{\mathrm{*}}$ and ${\mathrm{\sigma }}^{\mathrm{*}}$ excitons are localized primarily on the core-excited atom, but have significant weight on the nearest-neighbor atoms. The results are closely related to the electronic structure of a N impurity. © 1996 The American Physical Society.