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. (c) 2005 Elsevier B.V. All rights reserved.