ELECTRIC DOUBLE-LAYER PROPERTIES CALCULATED IN THE ANISOTROPIC REFERENCE HYPERNETTED-CHAIN APPROXIMATION

Double-layer interactions and ion density profiles are calculated in the anisotropic reference hypernetted chain (RHNC) approximation, which uses the RHNC approximation for the anisotropic ion-ion correlation functions in the double layer. The ion-ion bridge functions are taken from a hard sphere reference system with the same density profiles as the full system. Excellent agreement with simulation results is obtained even at high concentrations and surface charges. If the bridge functions are neglected (i.e. the anisotropic hypernetted chain (HNC) approximation is used) only qualitative agreement with simulation is obtained in regimes where the local ion density is high and the contributions from ion-ion correlations at short range are very important. Otherwise, both the anisotropic HNC and RHNC approximations give equally good results for the systems investigated. Some methodological questions for the RHNC calculations are discussed.