  The influence of the charging effects on the transport characteristics of a
molecular wire bridging two metallic electrodes in the limit of weak contacts
is studied by generalized Breit-Wigner formula. Molecule is modeled as a
quantum dot with discrete energy levels, while the coupling to the electrodes
is treated within a broad band theory. Owing to this model we find
self-consistent occupation of particular energy levels and orbital energies of
the wire in the presence of transport. The nonlinear conductance and
current-voltage characteristics are investigated as a function of bias voltage
in the case of symmetric and asymmetric coupling to the electrodes. It is shown
that the shape of that curves are determined by the combined effect of the
electronic structure of the molecule and by electron-electron repulsion.
