X-ray absorption spectra at the Ca-L$_{2,3}$-edge calculated within multi-channel multiple scattering theory

TL;DR

This paper introduces a new theoretical approach combining multi-channel multiple scattering theory and the eigen-channel R-matrix method to accurately compute X-ray absorption spectra, including electron correlation effects, demonstrated on calcium compounds.

Contribution

A novel computational method for XAS that incorporates electron correlation effects within a multi-channel multiple scattering framework, improving accuracy over existing models.

Findings

Successfully applied to Ca L-edge spectra in various compounds

Achieved good agreement with experimental data

Efficient computation with minimal additional cost

Abstract

We report a new theoretical method for X-ray absorption spectroscopy (XAS) in condensed matter which is based on the multi-channel multiple scattering theory of Natoli et al. and the eigen-channel R-matrix method. While the highly flexible real-space multiple scattering (RSMS) method guarantees a precise description of the single-electron part of the problem, multiplet-like electron correlation effects between the photo-electron and localized electrons can be taken account for in a configuration interaction scheme. For the case where correlation effects are limited to the absorber atom, a technique for the solution of the equations is devised, which requires only little more computation time than the normal RSMS method for XAS. The new method is described and an application to XAS at the Ca $L_{2,3}$-edge in bulk Ca, CaO and CaF$_2$ is presented.