  We present first principles calculations based on density functional theory
for the conductance of monatomic Al wires between Al(111) electrodes. In
contrast to the even-odd oscillations observed in other metallic wires, the
conductance of the Al wires is found to oscillate with a period of 4 atoms as
the length of the wire is varied. Although local charge neutrality can account
for the observed period it leads to an incorrect phase. We explain the
conductance behavior using a resonant transport model based on the electronic
structure of the infinite wire.
