Global minima of water clusters (H2O)n, n≤21, described by an empirical potential

Candidates are presented for the global minima of water clusters (H2O)n, n≤21, bound by the empirical rigid-body TIP4P potential. The TIP4P global minima were subsequently relaxed subject to a more sophisticated model potential of the ASP family. Candidates for the lowest energy `box-kiteʹ and dodecahedral minima of (H2O)20 have also been obtained. For both the TIP4P and ASP potentials the lowest-lying dodecahedral isomers have much higher energies than the lowest-lying box-kite and face-sharing pentagonal prismatic minima, in contrast to the results of recent semi-empirical molecular orbital calculations.