Conductance, contacts, and interface states in single alkanedithiol molecular junctions

We calculate the conductance of Au-alkanedithiol-Au molecular junctions from first principles, finding agreement with measured data for junctions where the terminal S atoms are attached to top sites of the gold electrodes. A major effect of the contact geometry on the conduction properties is found, whose origin is traced to the symmetry and spatial localization of the interface states. The implications of our finding to ongoing experiments are noted.