The isomers of the water hexamer play a major role in both experimental and theoretical studies of water clusters. The lowest energy isomers are non-cyclic. The energies of eight isomers have become a standard test of the fidelity of a water FF. A detailed analysis of the electronic energies of the eight isomers is given Table . The electronic dissociation energies, D e , for q-AQUA-pol are in better agreement the benchmark CCSD(T) result than MB-pol, which is in good agreement with the benchmarks for D e and the many-body interactions.