  For adjusting the charging state of a molecular metal complex in the context
of a density functional theory description of coherent electron transport
through single molecule junctions, we correct for self interaction effects by
fixing the charge on a counterion, which in our calculations mimics the effect
of the gate in an electrochemical STM setup, with two competing methods, namely
the generalized $\Delta$ SCF technique and screening with solvation shells. One
would expect a transmission peak to be pinned at the Fermi energy for a nominal
charge of +1 on the molecule in the junction but we find a more complex
situation in this multicomponent system defined by the complex, the leads, the
counterion and the solvent. In particular equilibrium charge transfer between
the molecule and the leads plays an importanty role, which we investigate in
dependence on the total external charge in the context of electronegativity
theory.
