Water nanodroplets: predictions of five model potentials

Putative global minima for five intermolecular potential energy models are reported for water clusters (H2O)n with n ≤ 55. The models studied include three empirical, pairwise-additive potential energy surfaces, TIP4P, TIP4P-Ew, and TIP4P/2005, which use fixed point charges and rigid monomers. The other two, TTM2.1-F and AMOEBA, are polarizable, include non-additive inductive effects, have flexible monomers, and were parametrized, at least partially, using ab initio data. The n = 51 cluster has the same structure and is exceptionally stable for all five potentials. A structured inner core can be seen in cage clusters with n > 37. Periplanar rings, branched rings, and coils are among the structural motifs of the inner core.