Coulomb repulsion and correlation strength in LaFeAsO from density functional and dynamical mean-field theories.

ABSTRACT

The LDA+DMFT (local density approximation combined with dynamical mean-field theory) computation scheme has been used to calculate spectral properties of LaFeAsO-the parent compound of the new high-T(c) iron oxypnictides. The average Coulomb repulsion [Formula see text] and Hund's exchange J parameters for iron 3d electrons were calculated using the first-principles constrained density functional theory scheme in the Wannier functions formalism. Resulting values strongly depend on the number of states taken into account in the calculations when the full set of O-2p, As-4p and Fe-3d orbitals and the corresponding bands are included, the interaction parameters [Formula see text] eV and J = 0.8 eV are obtained. In contrast, when the basis set is restricted to the Fe-3d orbitals and bands only, the calculation gives much smaller values of [Formula see text] eV, J = 0.5 eV. Nevertheless, DMFT calculations with both parameter sets and the corresponding basis sets result in a weakly correlated electronic structure that is in agreement with the experimental x-ray and photoemission spectra.