The current-voltage characteristic of a metal-molecule-metal junction studied by an integrated and piecewise thermal equilibrium approach

The current-voltage characteristic of a metal-molecule-metal junction has been studied by a new approach. The Au electrodes are modeled by 3-layer (111) films and the self-assembled monolayer (SAM) of Au-benzene-1,4-dithiol-molecule-Au molecules is sandwiched between them. The non-equilibrium electron distribution function is approximated by the Fermi-Dirac distribution function with a position dependent chemical potential to reflect spatial variation of the local electrostatic potential. The electronic states of the whole Au-film-SAM-Au-film system are calculated and are regarded as standing waves, which can be decomposed into +z and --z moving waves, $\Psi_{+}$ and $\Psi_{-}$, respectively, where z is the coordinate normal to the films. The current per molecule is obtained from the standard quantum mechanical current densities of the $\Psi_{+}$ and $\Psi_{-}$ states. With this approach the calculated I-V characteristic is improved substantially with respect to those obtained by the conventional transmission-probability-Green-function type approaches..