Impacts of metal electrode and molecule orientation on the conductance of a single molecule

We present first-principles investigation of electrical conductance of a benzene-1,4-dithiolate (-S-C6H4-S-) molecule bridging the (111) surfact of Pt and Au carried out using the Lippmann-Schwinger scattering method combined with the density functional theory. We show that Pt makes better electrodes than noble metals, due to a closer positioning of the transmission resonance to the Fermi level. Interestingly, we find that the peak transmission corresponding to the highest occupied molecular orbital decreases with the increasing of the tilting angle of the benzene dithiolate. Moreover, the flattening comes together with a widening of the peak, and consequently, the transmission at the Fermi level is enhanced. (C) 2004 American Institute of Physics.