Theoretical study of electron transport properties of bimolecular junctions: Effect of molecular arrangement and species

The electron-transport properties of several monomolecular and bimolecular junctions, which are based on cis-polyacetylene (PA) or fused pyrrole trimer (FP) molecule, are investigated by density functional theory (DFT) combined with nonequilibrium Green's function (NEGF). The calculated results show that the bimolecular conductance is usually greater than the monomolecular conductance. However, the monomolecular and bimolecular conductances are equivalent at the lower bias voltages. The conductance of bimolecular junction with intermolecular interaction is less than that without intermolecular interaction. The currents of PA bimolecular junction with “face-to-face” (FF) arrangement are greater than those with “face-to-face reversal” (FFR) arrangement. On the contrary, the currents of FP bimolecular junction with FF arrangement are less than those with FFR arrangement obviously. The conductive performance of bimolecular junctions with different arrangements shows good correlation with respective highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps. The transmission spectra, projected density of states, and molecular projected self-consistent Hamiltonian are employed to analyze the electron-transport properties.