  The origin of the quasi two-dimensional behavior of PdCoO2 and PtCoO2 is
investigated by means of electronic structure calculations. They are performed
using density functional theory in the generalized gradient approximation as
well as the new full-potential augmented spherical wave method. We show that
the electric conductivity is carried almost exclusively by the in-plane Pd (Pt)
d orbitals. In contrast, the insulating CoO2 sandwich layers of octahedrally
coordinated Co atoms may be regarded as charge carrier reservoirs. This leads
to a weak electronic coupling of the Pd (Pt) layers. The obtained nearly
cylindrical Fermi surface causes the strong anisotropy of the electric
conductivity.
