Electronic transport calculations for the conductance of Pt-1,4-phenylene diisocyanide-Pt molecular junctions

The low-bias transport properties of a single 1,4-phenylene diisocyanide (PDI) molecule connected to two platinum (Pt) electrodes are investigated using a self-consistent ab initio approach that combines the non-equilibrium Green's function formalism with density functional theory. Our calculations demonstrate that the zero-bias conductance of an asymmetric Pt-PDI-Pt junction, where the PDI molecule is attached to the atop site at one Pt(111) electrode and to a Pt adatom at the other, is 2.6 x 10-2G0, in good agreement with the experimental value (3 x 10-2G0) measured with break junctions. Although the highest occupied and the lowest unoccupied molecule orbitals in PDI are both π-type, delocalized along the entire molecule, their electronic coupling with the highly conducting states of the Pt electrode is blocked at the atop site, leading to the small transmission. This indicates that more efficient electronic contacts are needed to fabricate molecular devices with a high conductance using Pt electrodes and aromatic isocyanides such as PDI.