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

We have calculated rearrangement mechanisms for (H2O)8 and (H2O)20 clu sters by eigenvector following. For (H2O)8, two different parametrizat ions of a four-site, rigid water effective pair potential were conside red and found to give very similar results. Hence, only one of the pot entials 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 rearrangement s for both (H2O)8 and (H2O)20 are illustrated, with barrier heights ra nging over three orders of magnitude. The mechanisms range from almost imperceptible changes of geometry to folding processes that result in dramatic structural transformations.