Semiempirical investigations on the stabilization energies and ionic hydrogen-bonded structures of F^−(H2O)n and Cl^−(H2O)n (n = 1–4) clusters

Several semiempirical methods were utilized to analyze the structures and stabilities of x^−(h2o)n (x = f, cl; n = 1–4) clusters with respect to the number of water molecules through their comparison with ab initio molecular orbital calculations. our results show that the recently developed pm6-dh+ semiempirical method can provide reasonable binding energies of hydrated fluoride and chloride ion clusters, which are consistent with the corresponding experimental results. for the optimized geometries of x = f, however, the semiempirical methods show that the global minima are close to hf(oh)^−(h2o)n−1 structures, which are different from the ab initio calculations. meanwhile, the topological characteristics for the global minima of x = cl obtained by semiempirical methods have the same symmetries with ab initio calculations. all calculation levels agree on the trend of decreasing ion-water interaction with the increasing number of water molecules. we also found a new structure of cl^−(h2o)4 with a second hydration shell as a complement of previous studies. those are very important data for our near-future study of on-the-fly semiempirical molecular dynamics (md) or path integral md simulation.