Predictive simulations of core electron binding energies of halogenated species adsorbed on ice surfaces from relativistic quantum embedding calculations

TL;DR

This study uses relativistic quantum embedding combined with DFT and molecular dynamics to model core electron binding energies of halogenated species on ice, successfully reproducing experimental trends for L edges but underestimating environmental effects on K edges.

Contribution

It introduces a combined relativistic quantum embedding and DFT approach with temperature effects to accurately predict core electron binding energies in complex environments.

Findings

Reproduces experimental L edge trends on ice surfaces.

Underestimates environmental effects on K edges without correction.

Provides an ad hoc correction improving K edge energy predictions.

Abstract

We report an investigation of the suitability of quantum embedding for modeling the effects of the environment on the X-ray photoelectron spectra of hydrogen chloride and the chloride ions adsorbed on ice surfaces, as well as of chloride ions in water droplets. In our approach, we combine a density functional theory (DFT) description of the ice surface with that of the halogen species with the recently developed relativistic core-valence separation equation of motion coupled cluster (CVS-EOM-IP-CCSD) via the frozen density embedding formalism (FDE), to determine the K and L$_{1,2,3}$ edges of chlorine. Our calculations, which incorporate temperature effects through snapshots from classical molecular dynamics simulations, are shown to reproduce the experimental trends for L edges of the species on ice surfaces, with respect to changes in temperature as well as the decrease in core binding energies in Cl$^{-}$ with respect to HCl. Finally, we find that in contrast to the L edges, we strongly underestimate the environmental effects on the K edges. We trace this behavior to the inability of the embedding potential obtained with the FDE approach to faithfully reproduce the Kohn-Sham potential of the analogous DFT calculation on the whole (supermolecular) system, and provide an ad hoc correction to the CVS-EOM-IP-CCSD energies, based on ground-state DFT calculations, that yields binding energies with similar accuracy to that observed for the L edges.