Here we describe the recalibration of a force field for the sulfate (SO -2 4 ) ion in TIP4P/ water. We follow closely the procedure of Mamatkulov et al. , which consists in a double-optimization strategy based on the experimental ion solvation free energy and the experimental activity coefficients. The first step of this strategy consists in optimizing the Lennard-Jones (LJ) parameters of the oxygen atoms of SO -2