Proximity of antiferromagnetism and superconductivity in LaFeAsO1-xFx:: Effective Hamiltonian from ab initio studies

We report density functional theory calculations for the parent compound LaFeAsO of the recently discovered 26 K Fe-based superconductor LaFeAsO1-xFx. We find that the ground state is an ordered antiferromagnet, with staggered moment of about 2.3 mu(B), on the border with the Mott insulating state. We fit the bands crossing the Fermi surface, derived from Fe and As, to a tight-binding Hamiltonian using maximally localized Wannier functions on Fe 3d and As 4p orbitals. The model Hamiltonian accurately describes the Fermi surface obtained via first-principles calculations. Due to the evident proximity of superconductivity to antiferromagnetism and the Mott transition, we suggest that the system may be an analog of the electron-doped cuprates, where antiferromagnetism and superconductivity coexist.