TranSIESTA can compute electronic transport properties, such as the zero bias conductance and the I-V characteristic, of a nanoscale system in contact with two electrodes at different electrochemical potentials.
For more details on the formalism, see the main TranSIESTA:
“Density-functional method for nonequilibrium electron transport”, Mads Brandbyge, JoseLuis Mozos, Pablo Ordejón, Jeremy Taylor, and Kurt Stokbro, Phys. Rev. B 65, 165401 (2002).