Coulomb Parameter U and Correlation Strength in LaFeAsO
  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. 
V. I. Anisimov, Dm. M. Korotin, S. V. Streltsov, A. V. Kozhevnikov, J.   Kune\v{s}, A. O. Shorikov, M. A. Korotin