Electronic properties and Fermi surface for new Fe-free layered pnictide-oxide superconductor BaTi$_2$Bi$_2$O from first principles

Very recently, as an important step in the development of layered Fe-free pnictide-oxide superconductors, the new phase BaTi$_2$Bi$_2$O was discovered which has the highest $T_C$ (${\sim}\,4.6\,$K) among all related non-doped systems. In this Letter, we report for the first time the electronic bands, Fermi surface topology, total and partial densities of electronic states for BaTi$_2$Bi$_2$O obtained by means of the first-principles FLAPW-GGA calculations. The inter-atomic bonding picture is described as a high-anisotropic mixture of metallic, covalent, and ionic contributions. Besides, the structural and electronic factors, which can be responsible for the increased transition temperature for BaTi$_2$Bi$_2$O (as compared with related pnictide-oxides BaTi$_2$As$_2$O and BaTi$_2$Sb$_2$O), are discussed.