FIG. 3.

The geometry of the proposed dielectric boundary (DB) for a pair of ions (atoms) separated by a distance d < a_i + 2$r_w$ + a_j. Ions and water probe van der Waals surfaces, related to the corresponding van der Waals radii a_i, a_j, and $r_w$, are depicted by red and blue dashed lines, respectively. The DB of the ion pair is defined by the effective ionic (atomic) dielectric radii ρ_i and ρ_j, Eq. (12), and by the effective water probe dielectric radius ${\rho }_w$ which is specified by the distance from the SAS to the DB. For the solvent separated configurations (d > a_i + 2$r_w$ + a_j), the ion pair DB consists of two spheres of radii ρ_i and ρ_j.