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 for new high-Tc iron oxypnictides. Coulomb repulsion U and Hund's exchange J parameters for iron 3d electrons were calculated using \textit {first principles} constrained density functional theory scheme in Wannier functions formalism. Resulting values strongly depend on the number of states taken into account in calculations: when full set of O-2p, As-4p, and Fe-3d orbitals with corresponding bands are included, computation results in U=3÷4 eV and J=0.8 eV. In contrast to that when the basis set is restricted to Fe-3d orbitals and bands only, computation gives much smaller parameter values F0=0.8 eV, J=0.5 eV. However, DMFT calculations with both parameter sets and corresponding to them choice of basis functions result in weakly correlated electronic structure that is in agreement with experimental X-ray and photoemission spectra.
@article{arxiv.0810.2629,
title = {Coulomb repulsion and correlation strength in LaFeAsO from Density Functional and Dynamical Mean-Field Theories},
author = {V. I. Anisimov and Dm. M. Korotin and M. A. Korotin and A. V. Kozhevnikov and J. Kuneš and A. O. Shorikov and S. L. Skornyakov and S. V. Streltsov},
journal= {arXiv preprint arXiv:0810.2629},
year = {2009}
}