Global Minima of Water Clusters (H₂O)<i>_N</i>,<i>N</i>≤ 25, Described by Three Empirical Potentials

Abstract

We compare apparent global minimum structures of three widely used empirical point-charge models for water. These are SPC/E (Simple Point Charge/Extended), TIP3P (Transferable Intermolecular Potential 3 Point), and TIP4P. We obtain results for (H 2 O) N with N ≤ 25. We compute various quantities characterizing the clusters such as the average energy per molecule, the average oxygen-to-oxygen distance, the average hydrogen bond length and number, and the quantity μ 2 / V, where V is an effective cluster volume and μ is the cluster's dipole moment. The quantity μ 2 / V is interesting because it is approximately proportional to the free energy of solvation of a cluster in water. We also compare our genetic algorithm to the basin-hopping Monte Carlo method.