MINIMUM STRUCTURES AND DYNAMICS OF SMALL WATER CLUSTERS

Water clusters, (H2O)n, With n = 7-18 monomers, are studied with molecular dynamics methods and an empirical potential function which includes many-body polarization interactions. Minimum-energy geometries are obtained with the quenching technique and random initial conditions. It is shown that several minima have cubic-type arrangements of the oxygen atoms. These geometries may be considered as formed by the fusion of the cubic structures of the octamer and square tetramers and correspond either to stable minima or to minima with a cubic core surrounded by the extra molecules of the cluster. The dodecamer shows a special stability, and this and larger clusters guarantee an average hydrogen bond per water molecule close to the experimentally found value of 1.7 for liquid water. The power spectra of all cubic conformations show the low-frequency band observed in the millimeter region. A possible association of the stability of these multicubic clusters with the peculiar properties of liquid water is discussed.