With the ultimate purpose of designing molecule/surface interaction potentials for the dynamical study of electropolymerization reactions, a theoretical framework, based on density functional theory (DFT), is proposed to obtain in a self-consistent manner the true electronic density of a metallic surface set under an applied voltage. A direct link is made between the DFT chemical potential mu and the (experimental) electrode potential drop Delta epsilon imposed in electrochemical experiments. An emphasis is made on the possibility of using cluster models to describe polarized surfaces. It is found that within "experimental" applied voltages, the induced surface charges may be lower that previously expected. This suggests that the electrostatic component in molecule/ polarized-surface interaction potentials may not be overwhelmingly important towards other terms such as polarization, dispersion or even quantum contributions. In this respect, the mu=f(Delta epsilon) equation suggests that the Lewis acidic or basic character of a metallic surface can be monitored continuously by simply tuning the electrode potential drop. Possible experimental verifications of this proposal are examined.