Control of substituent ligand over current through molecular devices: An ab initio molecular orbital theory

We explain the order of current curves of the ligand-substituent benzene-derivative devices by an ab initio molecular orbital theory on the basis of the first-principles density functional theory and the nonequilibrium Green function technique. The results of our calculation show the control of the substituent ligand over electronic transport through the molecular device. Contrary to the Hückel tight-binding result, we find that both the LUMO and LUMO+1 of the extended molecule (the benzene derivative pluses one gold atom on each side) are localized states, which have no contribution to transport. It is straightforward to extend the full molecular orbital theory to any electrode-molecule-electrode system.