Proximity of antiferromagnetism and superconductivity inLaFeAsO1−xFx: Effective Hamiltonian fromab initiostudies

We report density functional theory calculations for the parent compound LaFeAsO of the recently discovered 26 K Fe-based superconductor ${\text{LaFeAsO}}_{1-x}{\text{F}}_x$. 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 $\text{Fe}3d$ and $\text{As}4p$ 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.