Electronic structure and dx2-y2-wave superconductivity in FeS

We perform theoretical studies on the newly discovered superconductor FeS. Using density functional theory, we obtain the electronic structure of FeS. Using maximally localized Wannier functions, we obtain an effective tight-binding model with five Fe 3d orbitals. Based on this model, we investigate, by the unbiased singular-mode functional renormalization group, the superconductivity derived from correlation effects. We find the Hund's rule coupling plays a key role in triggering superconductivity, and the pairing symmetry is d(x2-y2) wave (viewed in the unfolded zone). The gap function is nodal/nodeless on the hole/electron Fermi pockets, similarly to the case in LaOFeP. The nodal gap is in agreement with experiments.