Electronic properties of the FeSe/STO interface from first-principle calculations

Compared to experiment, the calculated bulk lattice constant of FeSe is too small in LDA, PBEsol and PBE type exchange-correlation (xc) functionals even though the mismatch decreases from LDA to PBE. In bulk SrTiO3 (STO) on the other hand LDA over-binds, PBE under-binds and PBEsol agrees best with experiment. With the errors in opposite directions, the strain in the FeSe monolayer on STO depends on the xc functional and, especially in the non-magnetic state, is strongly overestimated. In this work we investigate the influence of the xc functional and magnetism in density functional calculations on electronic bonding properties and charge transfer in the FeSe monolayer on a STO substrate. Furthermore, we consider the effect of oxygen-vacancies within the virtual crystal approximation. In agreement with earlier work, we find that the band structure of the checkerboard antiferromagnetic configuration agrees best with experiment where, in addition, the relative strain on FeSe is best described. For a small vacancy concentration, in agreement with recent experiment, the FeSe monolayer Ti layer distance increases while for higher concentrations it decreases.