Study of water clusters in the n = 2–34 size regime, based on the ABEEM/MM model

Abstract

Various properties of water clusters in the n = 2–34 size regime with the change of cluster size have been systemically explored based on the newly developed flexible-body and charge-fluctuating ABEEM/MM water potential model. The ABEEM/MM water model is to take ABEEM charges of all atoms, bonds, and lone-pairs of water molecules into the intermolecular electrostatic interaction term in molecular mechanics. The computed correlating properties characterizing water clusters (H2O)n (n = 2–34) include optimal structures, structural parameters, ABEEM charge distributions, binding energies, hydrogen bonds, dipole moments, and so on. The study of optimal structures shows that the ABEEM/MM model can correctly predict the following important structural features, such as the transition from two-dimensional (from dimer to pentamer) to three-dimensional (for clusters larger than the hexamer) structures at hexamer region, the transition from cubes to cages at dodecamer (H2O)12, the transition from all-surface (all water molecules on the surface of the cluster) to one water-centered (one water molecule at the center of the cluster, fully solvated) structures at (H2O)17, the transition from one to two internal molecules in the cage at (H2O)33, and so on. The first three structural transitions are in good agreement with those obtained from previous work, while the fourth transition is different from that identified by Hartke. Subsequently, a systematic investigation of structural parameters, ABEEM charges, energetic properties, and dipole moments of water clusters with increasing cluster size can provide important reference for describing the objective trait of hydrogen bonds in water cluster system, and also provide a strong impetus toward understanding how the water clusters approach the bulk limit.