We assessed the relative merits of two approaches for including polarization effects in classical force fields for the sulfate
anion. One of the approaches is the explicit shell model for atomic polarization and the other is an implicit dielectric continuum
representation of the electronic polarization, wherein the polarizability density is spatially uniform. Both the solvation and ion
association properties of sulfate were considered. We carried out an ab initio molecular dynamics simulation for a single sulfate
anion in aqueous solution to obtain a benchmark for the solvation structure. For the ion-pairing properties, the models were compared
to experimental thermodynamic data through Kirkwood-Buff theory, which relates the integrals of the pair correlation functions
to measurable properties. While deficiencies were found for both of the approaches, the continuum polarization model was not
systematically worse than the shell model. The shell model was found to give a more structured solution than the continuum
polarization model, both with respect to solvation and ion pairing.