REARRANGEMENTS OF MODEL (H2O)8 AND (H2O)20 CLUSTERS

We have calculated rearrangement mechanisms for (H2O)8 and (H2O)20 clusters by eigenvector following. For (H2O)8, two different parametrizations of a four-site, rigid water effective pair potential were considered and found to give very similar results. Hence, only one of the potentials is applied to (H2O)20. 6N-6 internal coordinates are required to describe a (H2O)N cluster in these calculations, of which 3N-6 were chosen as center-of-mass distances, angles, and dihedral angles, the other 3N being Euler angles. A wide variety of different rearrangements for both (H2O)8 and (H2O)20 are illustrated, with barrier heights ranging over three orders of magnitude. The mechanisms range from almost imperceptible changes of geometry to folding processes that result in dramatic structural transformations.