Theoretical X-ray Absorption Spectroscopy of Liquid Water by the GW plus Bethe-Salpeter equation (GW-BSE) method*

Oxygen K-edge x-ray absorption spectroscopy (XAS) provides an important local probe of the H-bond network in liquid water. Theoretical calculations of XAS spectra demand accurate modeling of both the molecular structure and the electron-hole excitation process. We generate the water structure from path-integral DeePMD calculations, whose neural network potential is trained on state-of-the-art DFT data at the SCAN0 hybrid functional level. Based on the above equilibrated trajectory, the XAS spectra of liquid water are computed by solving the Bethe-Salpeter equation (BSE) as implemented in the BerkeleyGW package. Our calculated XAS spectra of water agree well with experiments. Our results indicate that self-consistent GW quasiparticle wavefunctions and local-fields effects in electronic screening are crucial in the GW-BSE approach in order to yield XAS spectra that are in quantitative agreement with experiments.