On the compatibility of the Madrid-2019 force field for electrolytes with the TIP4P/Ice water model

The Madrid-2019 force field was recently developed to perform simulations of electrolytes in water. The model was specifically parameterized for TIP4P/2005 water and uses scaled charges for the ions. In this work, we test the compatibility of the Madrid-2019 force field with another water model: TIP4P/Ice. We shall denote this combination as Madrid-2019(TIP4P/Ice) force field. The key idea of this combination is to keep the ion-ion (Madrid-2019) and water-water (TIP4P/Ice) interactions unaltered with respect to the original models and taking the Lennard-Jones parameters for the ion-water interactions from the Madrid-2019 force field. By implementing this approach, we have maintained a reasonably good performance of the model regarding the densities and structural features of aqueous solutions, albeit yielding a moderately higher viscosity than the original model. However, the standout achievement of this new combination lies in its effective reproduction of the absolute values of the freezing temperatures of a number of ionic aqueous solutions, which could also be useful when studying hydrate formation from a two-phase system containing an aqueous solution in contact with a gas.