A first-principle calculation of the XANES spectrum of Cu$^{2+}$ in water

TL;DR

This paper presents a first-principles computational method using density functional theory to accurately simulate the XANES spectrum of Cu2+ in water, accounting for structural fluctuations and matching experimental data.

Contribution

The study introduces a novel first-principles approach for calculating XANES spectra that incorporates structural variability, improving interpretation of experimental spectra.

Findings

Cu2+ prefers a square-pyramidal geometry in water

The method accurately reproduces experimental XANES spectra

Structural fluctuations significantly influence spectral features

Abstract

The progress in high performance computing we are witnessing today offers the possibility of accurate electron density calculations of systems in realistic physico-chemical conditions. In this paper, we present a strategy aimed at performing a first-principle computation of the low energy part of the X-ray Absorption Spectroscopy (XAS) spectrum based on the density functional theory calculation of the electronic potential. To test its effectiveness we apply the method to the computation of the X-ray Absorption Near Edge Structure part of the XAS spectrum in the paradigmatic, but simple case of Cu2+ in water. In order to keep into account the effect of the metal site structure fluctuations in determining the experimental signal, the theoretical spectrum is evaluated as the average over the computed spectra of a statistically significant number of simulated metal site configurations. The comparison of experimental data with theoretical calculations suggests that Cu2+ lives preferentially in a square-pyramidal geometry. The remarkable success of this approach in the interpretation of XAS data makes us optimistic about the possibility of extending the computational strategy we have outlined to the more interesting case of molecules of biological relevance bound to transition metal ions.