  In this paper we compare different force fields that are widely used
(Gromacs, Charmm-22/x-Plor, Charmm-27, Amber-1999, OPLS-AA) in biophysical
simulations containing aqueous NaCl. We show that the uncertainties of the
microscopic parameters of, in particular, sodium and, to a lesser extent,
chloride translate into large differences in the computed radial-distribution
functions. This uncertainty reflects the incomplete experimental knowledge of
the structural properties of ionic aqueous solutions at finite molarity.We
discuss possible implications on the computation of potential of mean force and
effective potentials.
