First-Principles Investigation of Strong Excitonic Effects in Oxygen 1s X‑ray Absorption Spectra

Abstract

We calculated the oxygen 1s X-ray absorption spectra (XAS) of acetone and acetic acid molecules in vacuum by utilizing the first-principles <i>GW</i>+Bethe–Salpeter method with an all-electron mixed basis. The calculated excitation energies show good agreement with the available experimental data without an artificial shift. The remaining error, which is less than 1% or 2–5 eV, is a significant improvement from those of time-dependent (TD) density functional methods (5% error or 27–29 eV for TD-LDA and 2.4–2.8% error or 13–15 eV for TD-B3LYP). Our method reproduces the first and second isolated peaks and broad peaks at higher photon energies, corresponding to Rydberg excitations. We observed a failure of the one-particle picture (or independent particle approximation) from our assignment of the five lowest exciton peaks and significant excitonic or state-hybridization effects inherent in the core electron excitations