The potential of zero charge of a metal electrode and the surface potential of water from simulations

In the absence of specific adsorption, the potential of zero charge (pzc) is a characteristic of the interface. The pzc involves the inner and the surface potential of the solution. Highlevel quantum-chemical calculations give a high positive value of about 3.5 V, which is caused by the strongly localized nuclear charge. These values are in line with high-energy electron studies, but not with electrochemistry. A careful DFT study and classical force field simulations suggest, that the electrochemical value is about -0.5 V. All DFT simulations that have been published give good values for the pzc when compared with experiment, but have problems with the surface potential. Referring the pzc directly to the standard hydrogen electrode avoids the problem with the surface potential. We also suggest to calculate the pzc through the derivative of the surface energy with charge, which would avoid this problem.