  X-ray absorption spectroscopy (XAS) is a powerful experimental tool to probe
the local structure in materials with the core hole excitations. Here, the
oxygen K-edge XAS spectra of the NaCl solution and pure water are computed by
using a recently developed GW-BSE approach, based on configurations modeled by
path-integral molecular dynamics with the deep-learning technique. The neural
network is trained on ab initio data obtained with SCAN density functional
theory. The observed changes in the XAS features of the NaCl solution, compared
to those of pure water, are in good agreement between experimental and
theoretical results. We provided detailed explanations for these spectral
changes that occur when NaCl is solvated in pure water. Specifically, the
presence of solvating ion pairs leads to localization of electron-hole
excitons. Our theoretical XAS results support the theory that the effects of
the solvating ions on the H-bond network are mainly confined within the first
hydration shell of ions, however beyond the shell the arrangement of water
molecules remains to be comparable to that observed in pure water.
