Hydration and coordination of K+ solvation in water from ab initio molecular-dynamics simulation

Potassium ion in water plays a very important role in chemistry and biology. In this paper, we investigated the hydration structure and coordination of K+ solvation in water at 300 and 450 K using ab initio Car-Parrinello molecular dynamics. The K+-oxygen radial distribution function indicated that the perturbation of K+ on the water structure is strong in the first hydration shells, while it is mild outside of this region in normal liquid. According to our natural geometric criterion for the coordinated oxygen atom, the average coordination number of K+ is 6.24 and 6.53 at 300 and 450 K, respectively, which agrees with the experimental value (6.1). This geometric criterion can also be used to define strong, moderate and weak hydrogen bonds in liquid.