  We present results of electronic structure calculations for aluminium
contacts of atomic size, based on density functional theory and the local
density approximation. Addressing the atomic orbitals at the neck of the
nanocontact, we find that the local band structure deviates strongly from bulk
fcc aluminium. In particular, hybridization between Al 3s and 3p states is
fully suppressed due to directed bonds at the contact. Moreover, a charge
transfer of 0.6 electrons off the contact aluminium site is found. Both the
suppressed hybridization and the violated charge neutrality are characteristic
features of metallic nanocontacts. This fact has serious consequences for
models aiming at a microscopic description of transport properties.
