Effects of metal–molecule interface conformations on the electron transport of single molecule

The electron transport effects of molecule locations on the metal interface are investigated through metal–molecule–metal systems using the first principles method, based on density functional theory with norm conserving non-local pseudopotentials and non-equilibrium Green’s functions. Three kinds of molecule–metal interface conformations are studied. These include locating the molecule on the top, at the hollow site and on the bridge of metal surface atoms. Au–molecule–Au open systems are constructed and numerically examined where Au electrodes are described through a 3-D atomic model. The current–voltage characteristics, density of states and transmission functions of constructed systems are calculated and analyzed. Simulated results show that the on-atom contact exhibits the best molecule–metal coupling when an external bias lower than 1.4 V is applied. The bridge contact has a similar coupling as the hollow contact with a small difference at larger external bias. This may partially explain why experimental results have poor repeatability.