Monte Carlo simulation of the structural properties of concentrated aqueous alkali halide solutions at 25 °C using a simple civilized model

Abstract

In this paper we present the results of a Monte Carlo (MC) simulation study of the structural properties of concentrated aqueous solutions of various alkali halides at 25 °C using a simple civilized model (SCM). A simplified version of the rigid nonpolarizable SPC model of liquid water, in which the Lennard-Jones interaction between intermolecular oxygen sites is changed into a hard-core repulsion, is combined in our SCM with a treatment of the ions as charged hard spheres. Changes in the structure of the solvent, and the behavior of ionic solvation and ion pairing upon varying the concentration and size of the ions, are determined by computing the corresponding ten radial distribution functions from sufficiently long MC simulation runs for various aqueous alkali halide solutions at concentrations above 1 M. Hydration numbers are reported for the first time for NaBr and KBr, and the first simulation-based estimates for LiBr, NaI, and KI are also obtained. Whenever possible, results for the hydration numbers are compared with available experimental data and also with other simulation studies. The excellent predictive capability and simplicity of the SCM proposed here, should lead to the development of tractable theoretical approaches to aqueous 1:1 electrolyte solutions in the near future.