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

Abstract

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-T c iron oxypnictides. Coulomb repulsion U and Hund's exchange J parameters for iron 3d electrons were calculated using 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 F 0 =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.

Resonant inelastic x-ray scattering study of charge excitations in superconducting and nonsuperconducting PrFeAsO1−y

“…Our constraint on the value of U is consistent with the previous estimates for the 1111 system reported so far ranging between about 2 and 4 eV. [15][16][17][18] Now that we have determined the (U ,J) combination with J=0.2×U for PrFeAsO, we look at the dependences of the calculated spectrum on U and J for variations in U of ±1 eV and J of ±0.2 eV, in order to separately assess the respective roles of U and J. The results are shown in Fig.…”

Doping-dependent bandwidth renormalization and spin–orbit coupling in (Sr1−xLax)2RhO4

“…Smaller interaction strength in DMFT reflects the use of a smaller, t 2g -only, effective Hamiltonian, for which the interaction is screened more strongly than for Hamiltonians including all Rh 4d bands and O 2p states. [30] III. RESULTS AND DISCUSSION…”

Electronic structure of Fe-based superconductors

“…However, it is to be emphasized that density functional theory does already contain some correlations and as a result the addition of U can lead to double counting of correlations with detrimental effects in band-like metals. It should also be noted that arguments as to why correlation effects should be weak have been advanced by Nakamura and co-workers, [61] and also by Anisimov and co-workers, [62] based on a Wannier function analysis. In any case, considering the non-observation of the Hubbard bands and the non-observation of the associated strong spectral weight shifts into them as predicted by current DMFT calculations with substantial U we do not discuss these further here.…”