  The rate-equation approach is used to describe sequential tunneling through a
molecular junction in the Coulomb blockade regime. Such device is composed of
molecular quantum dot (with discrete energy levels) coupled with two metallic
electrodes via potential barriers. Based on this model, we calculate nonlinear
transport characteristics (conductance-voltage and current-voltage dependences)
and compare them with the results obtained within a self-consistent field
approach. It is shown that the shape of transport characteristics is determined
by the combined effect of the electronic structure of molecular quantum dots
and by the Coulomb blockade. In particular, the following phenomena are
discussed in detail: the suppression of the current at higher voltages, the
charging-induced rectification effect, the charging-generated changes of
conductance gap, and the temperature-induced as well as broadening-generated
smoothing of current steps.
