  Equilibrium structure, local densities of states, and electronic transport in
a gold nanowire made of a four-atom chain supported by two gold electrodes,
which has been imaged recently by high-resolution electron microscopy, and
chemical modification of the wire via the adsorption of a methylthiol molecule,
are investigated with ab-initio local density functional simulations. In the
bare wire at the imaged geometry the middle two atoms dimerize, and the
structure is strongly modified by the adsorption of the molecule with an
accompanying increase of the ballistic conductance through the wire.
