Density functional study of FeS, FeSe, and FeTe: Electronic structure, magnetism, phonons, and superconductivity

We report density functional calculations of the electronic structure, Fermi surface, phonon spectrum, magnetism, and electron-phonon coupling for the superconducting phase FeSe, as well as the related compounds FeS and FeTe. We find that the Fermi-surface structure of these compounds is very similar to that of the Fe-As based superconductors, with cylindrical electron sections at the zone corner, cylindrical hole surface sections, and depending on the compound, other small hole sections at the zone center. As in the Fe-As based materials, these surfaces are separated by a two-dimensional nesting vector at $(\ensuremath{\pi},\ensuremath{\pi})$. The density of states, nesting, and Fermi-surface size increase,…