Nuclear quantum effect on hydrogen bond network fluctuation in liquid water inferred by X-ray absorption spectra

Based on state of the art path-integral molecular dynamics simulations carried out with the MB-pol water model and calculations of electronic excitations within the self-consistent GW theory, we investigate nuclear quantum effects (NQEs) on the oxygen K-edge X-ray absorption spectra (XAS) of water at various temperatures. Under the influence of NQEs, protons are more delocalized, which significantly broadens the calculated XAS spectra. Furthermore, NQEs are responsible for nontrivial competing effects on the hydrogen bond network. On one hand, the liquid structure is slightly softened due to the presence of more broken hydrogen bonds. On the other hand, configurations with stronger hydrogen bonds are largely favored by proton delocalization. These competing NQEs yield important corrections on the calculated XAS spectra as demonstrated by red (blue) shifts of the main-edge (post-edge). The calculated XAS spectra are in nearly quantitative agreement with the available experimental data.