First-principle electronic structure calculations for magnetic moment in iron-based superconductors: An LSDA + negative U study

In order to resolve a discrepancy of the magnetic moment on Fe between the experimental and calculation results, we perform first-principle electronic structure calculations for iron-based superconductors LaFeAsO1-xFxLaFeAsO1-xFx in which x=0.0x=0.0 and x=0.125x=0.125 by using the LSDA + U framework. Consequently, we confirm in both the mother and doped compounds that negative U correction is crucial in matching the calculated magnetic moment with the observed one. A reason of the negative correction is that the Coulomb interaction on Fe orbitals is unexpectedly screened than LSDA’s expectation. We discuss which type of situation emerges when the negative U is a good correction in these compounds.