Multiplet ligand-field theory using Wannier orbitals

TL;DR

This paper presents a fast, ab initio multiplet ligand-field theory approach using Wannier orbitals, enabling efficient calculations of local properties in correlated insulators with results closely matching experimental data.

Contribution

It introduces a novel method combining Wannier orbitals with ligand-field theory to reduce computational costs and improve accuracy in modeling correlated materials.

Findings

Ligand orbitals effectively reduce Hilbert space size.

Calculated parameters agree within ~10% of experimental values.

Method successfully applied to NiO, MnO, and SrTiO3.

Abstract

We demonstrate how ab initio cluster calculations including the full Coulomb vertex can be done in the basis of the localized, generalized Wannier orbitals which describe the low-energy density functional (LDA) band structure of the infinite crystal, e.g. the transition metal 3d and oxygen 2p orbitals. The spatial extend of our 3d Wannier orbitals (orthonormalized Nth order muffin-tin orbitals) is close to that found for atomic Hartree-Fock orbitals. We define Ligand orbitals as those linear combinations of the O 2p Wannier orbitals which couple to the 3d orbitals for the chosen cluster. The use of ligand orbitals allows for a minimal Hilbert space in multiplet ligand-field theory calculations, thus reducing the computational costs substantially. The result is a fast and simple ab initio theory, which can provide useful information about local properties of correlated insulators. We compare results for NiO, MnO and SrTiO3 with x-ray absorption, inelastic x-ray scattering, and photoemission experiments. The multiplet ligand field theory parameters found by our ab initio method agree within ~10% to known experimental values.