What is the global minimum energy structure of the water hexamer? The importance of nonadditive interactions.

The global minimum energy structures of the water hexamer predicted by widely used analytic water potentials are very different from each other, while the cyclic hexamer does not appear to be a low-lying energy structure. However, high levels of ab initio calculation predict that a number of low-lying energy conformers including the cyclic conformer are almost all isoenergetic due to the balance of two-body and nonadditive interactions. For modeling of water potentials, we suggest that the binding energy of the dimer be between -5.0 and -4.7 kcal (mol dimer)-1, while the three-body corrections be taken into account to a large extent. [ABSTRACT FROM AUTHOR]