  We recently introduced a method based on density functional theory (DFT) and
non-equilibrium Green's function techniques (NEGF) for calculating the addition
energies of single molecule nano-junctions in the Coulomb blockade (CB) regime.
Here we apply this approach to benzene molecules lying parallel and at various
distances from two aluminum fcc (111) surfaces, and discuss the distance
dependence in our calculations in terms of electrostatic screening effects. The
addition energies near the surface are reduced by about a factor of two, which
is comparable to previously reported calculations employing a computationally
far more demanding quasi-particle description.
