Isotope effect in liquid water explored by X-ray absorption spectroscopy*

The X-ray absorption spectra (XAS) of both liquid H₂O and D₂O are computed using our recently developed approximate computational approach in solving Bethe-Salpeter equation. In the above, the molecular structures are obtained from the well-equilibrated trajectories generated by path-integral deep potential molecular dynamics (DPMD). In particular, the DPMD force field is constructed from ab initio path-integral molecular dynamics based on the strongly constrained and appropriately normed (SCAN) density functional. Our preliminary results indicate that the experimentally observed isotope effects in the XAS spectra are qualitatively reproduced by our theoretical prediction. The H-bond network in heavy water is slightly more structured than that in light water, which is consistent with the less prominent pre-edge and main-edge of theoretical XAS spectrum of D₂O than that of H₂O.