We utilize a density functional theory (DFT) based quantum mechanical/molecular mechanical (QM/MM) approach for the investigation of charge transfer (CT) excitation energies in molecule-metal systems. We perform calculations on a pyridine-Ag-20 system treating the most distant, with respect to pyridine, silver atoms using molecular mechanics by assigning atomic polarizabilities to each of these silver atoms. We investigate how additional silver layers affect the CT excitation energy and conclude that the CT excitation energy levels off while enlarging the silver cluster. (C) 2009 Elsevier B. V. All rights reserved.