Missteps in the Analytical Formula of Smaller-Ion Shell Model

Abstract

Recently, a smaller-ion shell (SiS) model was developed to describe the electrostatic interaction between ions in solutions (D. Fraenkel, Mol. Phys., 108, 1435 (2010)). The analytical formula based on the SiS model reproduces experimental data very well with only one fitting parameter (namely, ion size parameter, a). However, a numerical simulation of the SiS model does not agree with the analytical formula. This indicates that the analytical formula does not represent the SiS model correctly. Therefore, the ion size parameter (a) obtained by fitting Fraenkel’s analytical formula to the experimental data is physically meaningless.

Keywords

• electrolyte solution
• activity coefficient
• smaller-ion shell model
• poisson–boltzmann equation