Effects of field-induced geometry relaxation on the electron transport properties of 4,4′-biphenyldithiol molecular junction

The non-linear charge transport properties of 4,4′-biphenyldithiol molecular junction have been studied using the generalized Green's function theory. It is shown that the torsion angle between two phenyls is slightly decreased as increase of the external voltage while the whole molecule moves slightly along the reversed direction of the electric field. Calculations indicate that the inclusion of molecular geometry relaxation can avoid a false prediction of negative differential resistance behavior. The charge redistribution under the external bias results in resistive dipoles inside the molecule. The calculated I-V curves of 4,4′-biphenyldithiol molecular junction is consistent with experimental observations in some ways. The figure shows the conductance curve of 4,4′-biphenyldithiol molecular junction. The oscillating peaks of conductance are observed and the asymmetry of conductance curve related to the direction of applied bias is displayed. When the molecular geometry relaxation is included (dot line), the negative differential resistance behavior is not demonstrated.