Systematic computation of crystal field multiplets for X-ray core spectroscopies

TL;DR

This paper introduces a new method for calculating crystal field multiplets in X-ray spectroscopies, explicitly considering atomic positions and charges, enabling analysis of low symmetry environments and spectroscopic effects.

Contribution

The novel approach constructs crystal fields directly from atomic data, allowing flexible and accurate multiplet calculations for complex and low symmetry systems.

Findings

Accurate simulation of X-ray absorption and RIXS spectra without adjustable parameters.

Successful application to low symmetry environments like MnO and Dy complexes.

Predictions for RIXS spectra in specific low-temperature and molecular systems.

Abstract

We present a new approach to computing multiplets for core spectroscopies, whereby the crystal field is constructed explicitly from the positions and charges of surrounding atoms. The simplicity of the input allows the consideration of crystal fields of any symmetry, and in particular facilitates the study of spectroscopic effects arising from low symmetry environments. The interplay between polarization directions and crystal field can also be conveniently investigated. The determination of the multiplets proceeds from a Dirac density functional atomic calculation, followed by the exact diagonalization of the Coulomb, spin-orbit and crystal field interactions for the electrons in the open shells. The eigenstates are then used to simulate X-ray Absorption Spectroscopy and Resonant Inelastic X-ray Scattering spectra. In examples ranging from high symmetry down to low symmetry environment, comparisons with experiments are done with unadjusted model parameters as well as with semi-empirically optimized ones. Furthermore, predictions for the RIXS of low-temperature MnO and for Dy in a molecular complex are proposed.