Coulomb Screening Effects on Solvated Ions

Potentials of mean force of ions in solution are used to explore the energetics of solvation. From them, the stability of solvation states yields insight into how ions might behave in physical solution. However, results arising from simulations with different parameters frequently contradict. Decomposing the free energy of solvation into enthalpic and entropic contributions can help our understanding of what drives the energetic results obtained from any specific set of simulation parameters. Moreover, intuition of the effects ions have on the solution requires an understanding of the strength that ions are screened from the bulk. In an effort to model the effects of charge screening on ion pair stability, we present a linear response model that modifies the Coulomb potential and gives an alternate understanding of solvation transition barriers. Moreover, it predicts stable Coulombic pairings between like-charged ions, which we show exist in simulation. This allows us to better understand enthalpic contributions to the free energy of solvation, and helps to isolate entropic effects for further study.