Variational functional in local density approximation for coulombic electrolyte correlations in the electric double layer

Abstract

A classical coulombic correlation functional in one-loop (1L) and local-density-approximation (LDA) is derived for electrolyte solutions, starting from a first-principles many-body partition function. The 1L–LDA functional captures correlations between electrolyte ions and solvent dipoles, such as screening and solvation, which are ignored by conventional mean-field theories. This 1L–LDA functional introduces two parameters that can be tuned to the experimental dielectric permittivity and activity coefficients in the bulk electrolyte solution. The capabilities of the 1L–LDA functional for the description of metal–electrolyte interfaces are demonstrated by embedding the functional into a combined quantum–classical model. Here, the 1L–LDA functional leads to a more pronounced double-peak structure of the interfacial capacitance with higher peaks and shorter peak-to-peak distance, significantly improving the agreement with experimental data and showing that electrolyte correlation effects exert a vital impact on the capacitive response.