Dynamics and relaxation of an intermediate size water cluster (H2O)108

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Abstract
The potential surface, melting, surface structure, and hydrogen bond network of an intermediate size water cluster (H2O)108 are investigated. The orientation relaxations of single molecule and of collective molecules are analyzed and compared with those of liquid water. The collective orientation relaxation (COR) (i.e., dielectric relaxation) of the water cluster is found to be much faster than that of liquid water due to different boundary conditions. In both liquid and cluster, the cross correlation between individual molecular dipoles plays an important role in static and dynamic quantities. COR of the cluster yields a so‐called 1/f fluctuation in contrast to the well‐known Debye relaxation in liquid water. In order to understand these differences of COR between the water cluster and liquid water, the wave vector dependence of the transverse and longitudinal components of COR is examined. A surface effect on hydrogen bond network and the correlation between structural change and coordination number are analyzed.