Effects of dephasing in molecular transport junctions using atomistic first principles

We report a theoretical investigation of dephasing effects to quantum transport properties of molecular junctions. The quantum transport analysis is done by density functional theory carried out within the nonequilibrium Green's function framework, and the dephasing effect is modeled within the Büttiker-probe approach. We observe two distinct behaviors in the three systems we studied: either an increase or a decrease in electronic conduction with dephasing. For a 1,4-benzenedithiol molecule and an atomic gold chain, where the conducting molecular levels are located away from the Fermi level, conduction is seen to increase due to reduced destructive interference resulting from the Büttiker probe. On the other hand, for a very thin Al nanowire we find that backscattering dominates over the phase-randomization and the current decreases with dephasing. The resistance follows Ohm's law while the resistivity scales linearly with the scattering rate. Finally, a comparison between the Büttiker-probe model and a more microscopic dephasing model shows nearly identical transport characteristics. From a computational point of view, the Büttiker-probe model has an order of magnitude speed up. © 2009 The American Physical Society.link_to_subscribed_fulltex