  In this work, an extension of the Madrid-2019 force field is presented. We
have added the cations Rb + and Cs + and the anions F$^-$, Br$^-$ and I$^-$.
These ions were the remaining alkaline and halogen ions not previously
considered in the Madrid-2019 force field. The force field, denoted as
Madrid-2019-Extended, does not include polarizability, and uses the TIP4P/2005
model of water and scaled charges for the ions. A charge of 0.85 e is assigned
to monovalent ions. The force field developed provides an accurate description
of the aqueous solution densities over a wide range of concentrations up to the
solubility limit of each salt studied. Good predictions of viscosity and
diffusion coefficients are obtained for concentrations below 2 m. Structural
properties obtained with this force field are also in reasonable agreement with
the experiment. The number of contact ion pairs has been controlled to be low
so as to avoid precipitation of the system at concentrations close to the
experimental solubility limit. A comprehensive comparison of the performance
for aqueous solutions of alkaline halides of force fields of electrolytes using
scaled and integer charges is now possible. This comparison will help in the
future to learn about the benefits and limitations of the use of scaled charges
to describe electrolyte solutions.
