We present a first-principles calculation of the transmission eigenchannels
of an Al atomic wire between jellium electrodes. We show how the decomposi
tion of electronic states into eigenchannels can provide a transparent view
of electronic transport in atomic-sized systems. In particular, we show ho
w local density of states and current density resolved into eigenchannels r
eflect the atomic orbitals of the single Al atom. On the other hand, the ei
genchannel density of states has a one-dimensional (1D) band character for
the straight three-atom wire. From this we conclude that the transport thro
ugh the single Al atom in this case mainly has a 1D (channel) character in
contrast to a zero-dimensional resonant tunneling (dot) character.