X-ray absorption spectra of liquid, crystalline and amorphous phases of water

Based on approximate approach to the Bethe-Salpeter equations for electron-hole excitations, we calculate the oxygen K-edge spectra of liquid water, crystalline ices including hexagonal ice and ice VIII, as well as high density and low density amorphous ices. In the electron-hole excitation, we approximate the core hole as a frozen oxygen 1s state and calculate the excited electron by self-consistent quasi-particle wavefunction obtained from diagonalizing the static Coulomb hole plus screened exchange self-energy operator. Our molecular structures are generated with deep potential molecular dynamics whose neural network is trained from calculations of density functional theory with the SCAN meta-GGA functional approximation. For both the liquid and solid phases of water, pre-edge, main-edge and post-edge features are present. Our theoretical X-ray absorption spectra are in good agreement with available experiments in terms of both spectral position and spectral width.