A local density functional approximation for the ion distribution near a charged electrode in the restricted primitive model electrolyte

A local HNC/MSA approximation is developed and applied to the 1:1 restricted primitive model electrolyte. Improvement of ion density profiles in front of a charged electrode is achieved by employing ion—ion direct correlation functions from homogeneous systems of non-neutral composition as found locally in the inhomogeneous double layer. This approximation is related to the density functional approach for inhomogeneous fluids. The local HNC/MSA method predicts, at higher surface charges, layering of counterions and charge inversion as seen in Monte Carlo data, a strong increase of the surface potential with charging and a maximum in the double layer capacitance.