Abstract
We have performed the first-principles electronic structure calculation for the novel superconductor Ca 4 Al 2 O 6 Fe 2 As 2 which has the smallest a lattice parameter and the largest As height from the Fe plane among the Fe–As superconductors. We find that one of the hole-like Fermi surfaces is missing around the Γ point compared to the case of LaFeAsO. Analysis using the maximally-localized-Wannier-function technique indicates that the x y orbital becomes more localized as the As–Fe–As angle decreases. This induces rearrangement of bands, which results in the change of the Fermi-surface topology of Ca 4 Al 2 O 6 Fe 2 As 2 from that of LaFeAsO. The strength of electron correlation is also evaluated using the constraint RPA method, and it turns out that Ca 4 Al 2 O 6 Fe 2 As 2 is more correlated than LaFeAsO.
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