Asymmetric currents in a donor (D)-bridge (B)-acceptor (A) single molecule - revisit of the Aviram-Ratner diode

The quantum transport via a donor (D)-bridge (B)-acceptor (A) single molecule is studied using density functional theory in conjunction with the Landauer-B\"{u}ttiker formalism. Asymmetric electrical response for opposite biases is observed resulting in significant rectification in current. The intrinsic dipole moment induced by substituent side groups in the molecule leads to enhanced/reduced polarization of the system under a forward/reverse applied potential, thus asymmetry in the charge distribution and the electronic current under bias. Under a forward bias, the energy gap between the D and A frontier orbitals closes and the current increases rapidly; whereas under a reverse bias, the D-A gap widens and the current remains small.