Ab initio ligand field approach to determine electronic multiplet properties

TL;DR

This paper introduces a parameter-free ab initio method to calculate ligand field parameters and multiplet spectra of magnetic centers in solids, combining density functional theory with Wannier projections and exact diagonalization.

Contribution

The method uniquely derives ligand field parameters directly from DFT and Wannier functions, enabling accurate multiplet spectra predictions without empirical parameters.

Findings

Good agreement with experimental spectra for several compounds

Accurate determination of ligand field parameters from first principles

Applicable to 3d and 5f electron systems

Abstract

A method is developed to calculate the ligand field (LF) parameters and the multiplet spectra of local magnetic centers with open $d$- and $f$-shells in solids in a parameter-free way. This method proceeds from density functional theory and employs Wannier projections of nonmagnetic band structures onto local $d$- or $f$-orbitals. Energies of multiplets and optical, as well as X-ray spectra are determined by exact numerical diagonalization of a local Hamiltonian describing Coulomb, LF, and spin-orbit interactions. The method is tested for several 3$d$- and 5$f$-compounds for which the LF parameters and multiplet spectra are experimentally well known. In this way, we obtain good agreement with experiment for La$_2$NiO$_4$, CaCuO$_2$, Li$_2$CuO$_2$, ZnO:Co, and UO$_2$.