The individual and mean activity coefficients of an electrolyte from the inverse GCMC simulation

The grand-canonical Monte Carlo (GCMC) technique, which is primarily used to calculate the concentration of a solute for a given activity coefficient, can be inverted and applied to calculate the activity coefficients corresponding to a given concentration of a solute. The changes needed to be introduced in the GCMC algorithm are discussed in the paper. The new method called the inverse GCMC (IGCMC) technique is applied to calculate the mean activity coefficient of 1: 1, 2: 2, 2: 1, 3: 1 salts with equal and unequal ion sizes and over a wide range of the electrolyte concentrations. The results for equal ion sizes are compared with the corresponding data obtained from the GCMC of Valleau and Cohen. It is shown that the IGCMC technique, after some extensions, can be used to compute the individual ionic activity coefficients. A comparison is made with the Sloth and Sorensen individual activity results and with the theoretical predictions for the 1: 1 electrolyte with unequal ion sizes.