RECOVERING THE CONCEPT OF THE HYDRATED ION FOR MODELING IONIC-SOLUTIONS - A MONTE-CARLO STUDY OF ZN-2+ IN WATER

A [Zn(H2O)6]2+-H2O interaction potential has been developed by means o f ab initio calculations using the 3-21G basis sets. Monte Carlo simu lations of zinc ion in water have been performed by using the potentia l for the zinc hexahydrate and for comparative purposes that of Clemen ti developed for the single ion. Both simulations have used the same c onditions. Structural results derived from simulation of zinc hexahydr ate give a more disrupted second shell, with two maxima for the Zn-H r adial distribution function at the second shell. Results for the hydra tion energy of Zn2+ obtained from the hydrated ion approach (-518 kcal /mol) are much closer to the experimental estimation (-491 kcal/mol) t han results obtained with the potential for the single ion (-845 kcal/ mol). As a matter of fact, the main conclusion of this study is that t he MC and MD simulations of ions in solution using the concept of a sp ecies beyond the single ion is not unrealistic and can be, under some conditions, an interesting alternative to be considered in the case of conflicting simulations of highly charged or transition metal ions. A dvantages and limitations of this approximation are discussed.