Physical Chemical Properties of Uncharged Water Clusters and One-Dimensional Ice Based on Quantal Calculations

Progress on a variety of atmospheric problems requires a successful first-principles treatment of water cluster behavior. Here a systematic study is reported on the physical and chemical properties of finite water clusters as a function of size and on an infinite-sized cluster, i.e. ice, by modeling a one-dimensional crystal. A modified version of the semi-empirical quantum chemical technique MNDO, particularly well suited for hydrogen bonding, is used. The stability of the water clusters is examined at 0 K through binding energy considerations and a finite temperatures through free energy of formation information as given by statistical mechanical techniques. The effects of entropy are included. Information on these thermodynamics parameters for water clusters of large size is needed for an understanding of the atmospherically relevant heterogeneous nucleation process.