We present a simple model of electrical transport through a
metal-molecule-metal nanojunction that includes charging effects as well as
aspects of the electronic structure of the molecule. The interplay of a large
charging energy and an asymmetry of the metal-molecule coupling can lead to
various effects in non-linear electrical transport. In particular, strong
negative differential conductance is observed under certain conditions.Comment: 7 pages, 5 figures, accepted by Europhys. Let