Cube to cage transitions in (H2O)n (n512, 16, and 20)

Molecular dynamics computer simulations were performed for (H2O)n ~n512, 16, and 20! followed by systematic quenching under a polarizable and a nonpolarizable model to determine the minimum energy structures each favored. Ab initio calculations were done on several minima for ~H2O!12 to determine their relative energies. The polarizable model prefers cagelike structures for all cluster sizes, whereas the nonpolarizable model predicts minima of fused cubes for ~H2O!12 and ~H2O!16 but makes the transition to a cagelike minimum at ~H2O!20. © 1996 American Institute of Physics. @S0021-9606~96!50131-5#