  Recent molecular simulation and integral equation results alkali-halide ion
pair potentials-of-mean-force in water are discussed. Dielectric model
calculations are implemented to check that these models produce that
characteristic structure of contact and solvent-separated minima for oppositely
charged ions in water under physiological thermodynamic conditions. Comparison
of the dielectric model results with the most current molecular level
information indicates that the dielectric model does not, however, provide an
accurate description of these potentials-of-mean-force. We note that linear
dielectric models correspond to modelistic implementations of second-order
thermodynamic perturbation theory for the excess chemical potential of a
distinguished solute molecule. Therefore, the molecular theory corresponding to
the dielectric models is second-order thermodynamic perturbation theory for
that excess chemical potential. The second-order, or fluctuation, term raises a
technical computational issue of treatment of long-ranged interactions similar
to the one which arises in calculation of the dielectric constant of the
solvent. It is contended that the most important step for further development
of dielectric models would be a separate assessment of the first-order
perturbative term (equivalently the {\it potential at zero charge} ) which
vanishes in the dielectric models but is generally nonzero. Parameterization of
radii and molecular volumes should then be based of the second-order
perturbative term alone. Illustrative initial calculations are presented and
discussed.
