Towards the correct microscopic structure of aqueous CsCl solutions with a comparison of classical interatomic potential models

Abstract

The structure of aqueous CsCl solutions was investigated by classical molecular dynamics simulations (MD) at three salt concentrations (1.5, 7.5, and 15 mol %). Thirty interatomic potential sets, based on the 12-6 Lennard-Jones model, parametrized for non-polarizable water solvent molecules were collected and tested. Some basic properties, such as density, static dielectric constant, and self-diffusion coefficients, predicted by the force fields (FF), were compared with available experimental data. The simulated particle configurations were used to calculate the partial radial distribution functions (PRDF) and the neutron and X-ray total scattering structure factors (TSSF). The TSSFs were compared with experimental data from the literature, to find the best FF models, which describe the structure correctly. It was found that, though several of the thirty models failed in the tests, some models are compatible with the measured data. Values of the structural parameters consistent with the experiments were determined (such as water-ion distances, the average number of water molecules around the ions, average number, and distance between anion-cation contact ion pairs, water-water hydrogen bonds). It was shown, that in addition to models in which the number of contact ion pairs is too high, models in which this number is too low are also unable to reproduce the experimental data.