Most aqueous biological and technological systems contain solvated ions. Atomistic explicit-
water simulations of ionic solutions rely crucially on accurate ionic force fields, which contain
most commonly two adjustable parameters: the Lennard-Jones diameter and the interaction
strength. Assuming these parameters to be properly optimized, the plethora of parameters
one finds in the literature for one and the same ion is surprising. In principle, the two
parameters should be uniquely determined by matching two ionic properties obtained for a …