Understanding ion–ion interactions in bulk and aqueous interfaces using molecular simulations

In addition to its scientific significance, the distribution of ions in the bulk and at aqueous interfaces is also very important for practical reasons. Providing a quantitative description of the ionic distribution, and describing interactions between ions in different environments, remains a challenge, and is the subject of current debate. In this study, we found that interionic potentials of mean force (PMFs) and interfacial properties are very sensitive to the ion–ion interaction potential models. Our study predicted a Sr2+–Cl− PMF with no contact ion-pair state and a shallow solvent-separated ion-pair state. In addition, we were able to quantitatively capture the experimental X-ray reflectivity results of the aqueous salt interface of the Sr2+–Cl− ion-pair, and provided a detailed physical description of the interfacial structure for this system. We also predicted the X-ray reflectivity results for SrBr2 and SrI2 systems.