A new interaction potential for Cl-, Li+, Na+, and Ca+2 in methanol solutions using the scaled charges concept.

Abstract

The Madrid-2019 intermolecular potential was developed for use in molecular simulations of salty aqueous solutions. The selection of the accurate TIP4P/2005 potential for water and the adoption of scaled charges for ions, ±0.85e for monovalent ions and ±1.70e for divalent ions, are the key features of the model. The use of scaled charges enhances the description of several properties, including solubility, transport properties, the density maximum, and the water activity in ionic solutions. In this study, we will investigate the performance of scaled charges in describing the properties of inorganic salts containing Cl-, Li+, Na+, and Ca+2 in another polar solvent, methanol. The ion charges and ion-ion interactions were taken from the Madrid-2019 potential, while the accurate OPLS/2016 model was selected for methanol. The protocol used in the development of the Madrid-2019 model, particularly regarding the selection of target properties in the fitting procedure, was applied to create this potential using LiCl, NaCl, and CaCl2 as inorganic salts. Its predictive ability was evaluated by calculating the density, dielectric constant, self-diffusion coefficients of methanol and ions, and viscosity for methanolic solutions of these three salts. As will be shown, the experimentally observed effects of salt addition are reproduced by the new model, not only qualitatively but also quantitatively. Furthermore, since the interaction potential is compatible with the Madrid-2019 model, we also demonstrated its accurate predictive ability in the ternary system methanol + water + NaCl.