  The results of electronic structure calculations for the one-dimensional
magnetic chain compound Ca3Co2O6 are presented. The calculations are based on
density functional theory and the local density approximation and used the
augmented spherical wave (ASW) method. Our results allow for deeper
understanding of recent experimental findings. In particular, alternation of Co
3d low- and high-spin states along the characteristic chains is related to
differences in the oxygen coordination at the inequivalent cobalt sites. Strong
hybridization of the d states with the O 2p states lays ground for polarization
of the latter and the formation of extended localized magnetic moments centered
at the high-spin sites. In contrast, strong metal-metal overlap along the
chains gives rise to intrachain ferromagnetic exchange coupling of the extended
moments via the d_{3z^2-r^2} orbitals of the low-spin cobalt atoms.
