We present a continuum theory of electrolytes composed of a waterlike solvent and
univalent ions. First, we start with a density functional F for the coarse-grained solvent,
cation, and anion densities, including the Debye–Hückel free energy, the Coulombic
interaction, and the direct interactions among these three components. These densities
fluctuate obeying the distribution∝ exp (− F/k BT)⁠. Eliminating the solvent density deviation
in F⁠, we obtain the effective non-Coulombic interactions among the ions, which consist of …