Coulomb Parameter U and Correlation Strength in LaFeAsO

TL;DR

This study calculates Coulomb U and Hund's J parameters for iron 3d electrons in LaFeAsO using first principles methods, showing their dependence on the basis set and resulting in weakly correlated electronic structures consistent with experiments.

Contribution

It introduces a basis set-dependent calculation of Coulomb and Hund's parameters in LaFeAsO and links these to electronic correlation strength via LDA+DMFT.

Findings

U=3-4 eV with extended basis set

F^0=0.8 eV, J=0.5 eV with Fe-3d basis only

Results align with X-ray spectra indicating weak correlations

Abstract

First principles constrained density functional theory scheme in Wannier functions formalism has been used to calculate Coulomb repulsion U and Hund's exchange J parameters for iron 3d electrons in LaFeAsO. Results strongly depend on the basis set used in calculations: when O-2p, As-4p, and Fe-3d orbitals and corresponding bands are included, computation results in U=3-4 eV, however, with the basis set restricted to Fe-3d orbitals and bands only, computation gives parameters corresponding to F^0=0.8 eV, J=0.5 eV. LDA+DMFT (the Local Density Approximation combined with the Dynamical Mean-Field Theory) calculation with this parameters results in weakly correlated electronic structure that is in agreement with X-ray experimental spectra.