Voids and clusters in expanded water

Molecular-dynamics simulations of water at elevated temperatures and reduced densities relative to ambient conditions are used to examine the size distributions of suitably defined hydrogen bonded clusters, physical clusters, and voids. The cluster structure of both hydrogen bonded clusters and physical clusters changes rapidly as a function of density for near critical and supercritical temperatures. The density variation of an observable quantity, a local density, is shown to be a signature of the onset in the change in cluster size. The densities with a broad range of cluster sizes are roughly located in the supercritical temperature region. [S0021-9606(99)50304-8].