  Our analysis of the contact formation processes undergone by Au, Ag and Cu
nanojunctions, reveals that the distance at which the two closest atoms on a
pair of opposing electrodes jump into contact is, on average, two times longer
for Au than either Ag or Cu. This suggests the existence of a longer range
interaction between those two atoms in the case of Au, a result of the
significant relativistic energy contributions to the electronic structure of
this metal, as confirmed by ab initio calculations. Once in the contact regime,
the differences between Au, Ag and Cu are subtle, and the conductance of
single-atom contacts for metals of similar chemical valence is mostly
determined by geometry and coordination.
