  We have performed the first-principles electronic structure calculation for
the novel superconductor Ca4Al2O6Fe2As2 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 Gamma point compared to the case of LaFeAsO. Analysis using the
maximally-localized-Wannier-function technique indicates that the xy 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 Ca4Al2O6Fe2As2 from that of LaFeAsO. The strength of electron
correlation is also evaluated using the constraint RPA method, and it turns out
that Ca4Al2O6Fe2As2 is more correlated than LaFeAsO.
