DFT Computation of the Electronic Band Structure of FeSe

Abstract

We calculate the band structure of FeSe in the space group P4/nmm with unpolarized as well as with polarized orbitals. There is a tetrahedron of Se atoms inside the cell. The polarized Fermi energy is found to be −4.54 eV and the binding energy is −33.0 eV. The energy gap varies from 0.58 eV at Z point to 1.58 eV at R point. The gap is highly anisotropic. Next we make a unit cell of FeSe with two Se atoms removed. So that whereas there are 2 Se atoms in the perfect unit cell, there is only one Se atom in the doped cell. There is a pronounced effect on the density of states. We calculate the band structure for the unit cell with only one atom of Se per unit cell by using polarized as well as unpolarized orbitals. It is found that the gap is reduced by a large amount of energy in the unit cell with 1 Se atom compared with that with 2 Se atoms. The gap for 1 Se cell varies from 0.45 eV at G point to 1.0 eV at Q point. This reduced gap is conducive to superconductivity.