Density functional study of the overdoped iron chalcogenide TlFe2Se2 with ThCr2Si2 structure

We report density functional calculations of electronic structure and magnetic properties of ternary iron chalcogenide TlFe2Se2, which occurs in the ThCr2Si2 structure and discuss the results in relation to the iron-based superconductors. The ground state is antiferromagnetic with checkerboard order and Fe moment similar to 1.90 mu(B). There is strong magnetoelastic coupling similar to the Fe-based superconductors, reflected in a sensitivity of the Se position to magnetism. Tl is monovalent in this compound, providing heavy electron doping of 0.5 additional carriers per Fe relative to the parent compounds of the Fe-based superconductors. Other than the change in electron count, the electronic structure is rather similar to those materials. In particular, the Fermi surface is closely related to those of the Fe-based superconductors, except that the electron cylinders are larger, and the hole sections are suppressed. This removes the tendency toward a spin-density wave.