First-principles study of Fe-based superconductors: A comparison of screened hybrid functional with gradient corrected functional

The hybrid functional calculations have been shown to often make significant improvement over the local density approximation (LDA) and generalized gradient approximation (GGA) calculations on materials properties and to be frequently successful in strongly correlated systems where the LDA and GGA calculations fail. By using first-principles hybrid functional calculations, we have studied the atomic structures, electronic properties, and magnetic orders of two typical iron-based superconductor materials, BaFe2As2 and β-FeSe. The calculated results are reported and analyzed in comparison with GGA. Especially, the semimetal states in antiferromagnetic orders with GGA are shown to be semiconducting with the hybrid functional. The local magnetic moment of an Fe atom in antiferromagnetic states enlarges from 1.5–2.0 μB with GGA to 3.3–3.4 μB with hybrid functional, which is considered to be an intrinsic value. The present hybrid functional calculations that aim at improving the exchange interaction, in comparison with the otherwise beyond LDA/GGA calculations, shed new light on a fundamental issue of what respective role of exchange and correlation playing in transition-metal compounds.