ELECTRONIC STRUCTURE OF K0.8Fe2Se2 FROM DENSITY FUNCTIONAL THEORY GW METHOD SIMULATION.

First principles density functional theory — based (GW) method — was used to simulate the electronic structure of the novel iron-based superconductor K0.8Fe2Se2. The calculated band gap of K0.8Fe2Se2 at the Γ point is 0.15 eV, which is significantly lower than the 0.61 eV of vacancy free crystal KFe2Se2. The d-orbital of Fe atom is overlapped with the p-orbital of Se atom. Charge density analysis shows strong lattice distortion and vacancy related electric dipole and quadruple near the K vacancy. The reflectivity is anisotropic in three coordinate directions. [ABSTRACT FROM AUTHOR]