Electron-hole theory of the effect of quantum nuclei on the x-ray absorption spectra of liquid water

TL;DR

This study uses electron-hole excitation theory combined with path-integral molecular dynamics to reveal how quantum nuclear effects influence the X-ray absorption spectra of liquid water, showing significant differences from classical models and aligning well with experimental data.

Contribution

It introduces a quantum nuclear approach to accurately model water's X-ray spectra, highlighting the impact of nuclear quantum effects on spectral features and hydrogen bonding.

Findings

Quantum nuclei affect spectral energies and line shapes.

Quantum effects broaden the pre-edge spectra.

Spectra align closely with experimental observations.

Abstract

Electron-hole excitation theory is used to unveil the role of nuclear quantum effects on the X-ray absorption spectral signatures of water, whose structure is computed via path-integral molecular dynamics with the MB-pol intermolecular potential model. Compared to spectra generated from the classically modeled water, quantum nuclei introduce important effects on the spectra in terms of both the energies and line shapes. Fluctuations due to delocalized protons influence the short-range ordering of the hydrogen bond network via changes in the intramolecular covalence, which broaden the pre-edge spectra. For intermediate-range and long-range ordering, quantum nuclei approach the neighboring oxygen atoms more closely than classical protons, promoting an "ice-like" spectral feature with the intensities shifted from the main- to post-edge. Computed spectra are in nearly quantitative agreement with the available experimental data.