Assessment of the pairwise additive approximation and evaluation of many-body terms for water clusters

The accuracy of a set of density functional methods is evaluated for predicting the binding energies and many-body terms in a set of water clusters. The binding energies obtained from density functional theory (DFT) are compared to accurate pairwise additive energies obtained by using the very accurate-Weizmann-1 level of theory and these results have illustrated the importance of the choice of basis set used in simulation of bulk water and ice.