Monte Carlo simulation of F−(H2O)4 using an ab initio potential

We present results concerning the structure and energetics of the cluster F−(H2O)4 at 0 K, using high quality ab initio methods, and at a temperature of 300 K, using an ab initio Monte Carlo simulation. At 0 K, we find the global energy minimum corresponds to three waters solvating the fluoride ion and with the fourth water in an outer hydration shell, hydrogen bonding to the other water molecules. Structures involving four waters hydrogen bonding to the fluoride are, however, of only slightly higher energy. At 300 K, the simulation results indicate that the fluoride is mostly to be found within a tetrahedron of solvating water molecules. The cluster is mobile, however, and a wide variety of structures are sampled.