In this paper we report the geometries and properties of 24 structural isomers located on the MP2/6-311++g** potential energy surface of the water hexamer. At least 15 structural patterns are located within 3 kcal/mol of the most stable conformation, leading to a very complex potential energy surface, several isomers having significant contributions. A quadratic correlation between the distance from the proton to the center of the hydrogen bond with the distance between oxygen atoms for all clusters is reported. MP2/6-311++g** and CCSD(T)/aug-cc-pvdz//MP2/6-311++g** predict different stabilization orderings but are in good agreement for binding energies. Compact structures are energetically favored by electronic energies with zero point energy corrections, while noncompact cyclic structures are preferred when temperature and entropy are accounted for.

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In this paper we report the geometries and properties of 38 distinct geometrical motifs located on the B3LYP/6-31+G(d), MP2/6-311++G(d, p) potential energy surfaces of the water heptamer. Binding energies of up to 45 kcal/mol are calculated. All motifs fall within 10 kcal/mol of the most stable conformation, with at least 13 structural patterns located no more than 3 kcal/mol above, leading to a very complex potential energy surface, populated by a multitude of motifs each one allowing large numbers of conformations. Cluster stability does not seem to be correlated with the number of hydrogen bonds. Compact structures are energetically favored by electronic energies with zero-point energy corrections, while more open structures are preferred when temperature and entropy are accounted for. The molecular interactions holding the clusters as discrete units lead to large binding energies but are not strong enough to cause significant changes in the geometries of the interacting monomers. Our results indicate that bonding in the water heptamers can be considered as largely non-shared interactions with contributions from intermediate character of increasing covalency.