  By means of first-principles calculations, the electronic structure and
chemical bonding for the recently discovered tetragonal (s.g. P4/n; # 85)
superconducting (Tc ~ 25K) phase Ca10(Pt4As8)(Fe2As2)5 have been examined in
details, and the optimized structural parameters, electronic bands, densities
of states, and inter-atomic bonding picture were evaluated and analyzed in
comparison with related layered iron-based superconducting materials. We have
shown that (i) Ca10(Pt4As8)(Fe2As2)5 is metallic-like, and the electronic bands
in the window around the Fermi level are formed mainly by the Fe 3d states of
(Fe2As2)5 blocks; (ii) the (Pt4As8) blocks will behave as semi-metals with very
low densities of states at the Fermi level; (iii) the near-Fermi bands adopt a
"mixed" character: simultaneously with quasi-flat bands, a series of
high-dispersive bands which intersect the Fermi level was found; (iv) the of
chemical bonding in Ca10(Pt4As8)(Fe2As2)5 is very complicated and includes an
anisotropic mixture of covalent, metallic, and ionic inter-atomic and
inter-block interactions.
