  Although aqueous electrolytes are among the most important solutions, the
molecular simulation of their intertwined properties of chemical potentials,
solubility and activity coefficients has remained a challenging problem, and
has attracted considerable recent interest. In this perspectives review, we
focus on the simplest case of aqueous sodium chloride at ambient conditions and
discuss the two main factors that have impeded progress. The first is lack of
consensus with respect to the appropriate methodology for force field (FF)
development. We examine how most commonly used FFs have been developed, and
emphasize the importance of distinguishing between "Training Set Properties"
used to fit the FF parameters, and "Test Set Properties", which are pure
predictions of additional properties. The second is disagreement among
solubility results obtained, even using identical FFs and thermodynamic
conditions. Solubility calculations have been approached using both
thermodynamic--based methods and direct molecular dynamics--based methods
implementing coexisting solution and solid phases. Although convergence has
been very recently achieved among results based on the former approach, there
is as yet no general agreement with simulation results based on the latter
methodology. We also propose a new method to directly calculate the electrolyte
standard chemical potential in the Henry-Law ideality model. We conclude by
making recommendations for calculating solubility, chemical potentials and
activity coefficients, and outline a potential path for future progress.
