First-principles study of substituents effect on molecular junctions: Towards molecular rectification

The nonequilibrium Green’s function technique and density functional theory were used to perform ab initio quantum-mechanical calculations of electronic transport of single polyacetylene (PA) molecular wire sandwiched between two gold electrodes. To inspect the substituents effect on the electronic transport properties, both the electron-donating (–NH2) and electron-withdrawing (–NO2) groups were asymmetrically introduced into the conjugated PA molecular wire, resembling the semiconductor p–n junction. The results demonstrated the rectification behavior of the substituted PA. The asymmetric evolutions of the energy levels and spatial distributions of the frontier molecular orbitals with the applied voltage are found to be essential in generating this current–voltage asymmetry.