Siberian Federal University

Effect of the spin-orbit coupling on the band structure and the Fermi surface of the three- orbital model is studied. The inter-orbital part of the model is reformulated to fully conform with the iron lattice symmetry. Because there are two iron ions in the unit cell, we introduce the intra- and inter- ion spin-orbit coupling constants to separate the effect of the related couplings on the band structure and the Fermi surface. Both the intra- and inter-ion parts lift the degeneracy of some bands at the Γ = (0, 0) point and the splitting of bands along the (0, π) − (π, π) direction of the Brillouin zone. We show that the inter-ion part of the spin-orbit coupling leads to the topological change of the Fermi surface — the splitting of two Fermi surface sheets around the M = (π, π) point