Correlation Effects on Antiferromagnetism in Fe Pnictides

To investigate correlation effects on antiferromagnetic order in Fe pnictides, we apply a variational Monte Carlo method to a two-orbital model. We obtain a small ordered moment consistent with experimental observations even for a Coulomb interaction comparable to the band width. Studies of estimation of the Coulomb interaction for Fe pnictides suggest values comparable to or slightly smaller than the band width, and much larger ordered moments have been obtained by the Hartree-Fock approximation for such a large Coulomb interaction. Thus, the correlation effect is important for Fe pnictides at least quantitatively.