Resistive and rectifying effects of pulling gold atoms at thiol-gold   nano-contacts
  We investigate, by means of first-principles calculations, structural and transport properties of junctions made of symmetric dithiolated molecules placed between Au electrodes. As the electrodes are pulled apart, we find that it becomes energetically favorable that Au atoms migrate to positions between the electrode surface and thiol terminations, with junction structures alternating between symmetric and asymmetric. As a result, the calculated $\emph{IV}$ curves alternate between rectifying and non-rectifying behaviors as the electrodes are pulled apart, which is consistent with recent experimental results. 
Ronaldo J. C. Batista, Pablo Ordej\'on, H\'elio Chacham, and Emilio   Artacho