Ab initio study of near-edge x-ray absorption fine structure of hexagonal ice and liquid water

We report first-principles calculations of near-edge x-ray absorption fine structure (NEXAFS) spectra of hexagonal ice and liquid water. Our work is motivated by the importance of accurately modeling NEXAFS spectra, which provide sensitive information on local molecular structures. In particular, we find a systematic improvement in the agreement of the calculated spectra with the experiment, by including excitonic effects, final state and self-interaction corrections. We correlate the calculated corrections to the degree of localization of the excited states.