Global minima of water clusters (H2O)N, N ≤ 25, described by three empirical potentials

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 (H2O)(N) with N less than or equal to 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 mu(2)/V, where V is an effective cluster volume and mu is the cluster's dipole moment. The quantity mu(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.