Clusters of alkali halide molecules

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Abstract
The equilibrium geometry and formation energy of clusters (MX)n with n=1 to 44 and the vibrational spectrum of clusters with n=1 to 6 for a variety of alkali halides have been calculated using a simple shell model for the interionic forces. As n increases, the deviation of the binding energy and atomic volume from that of bulk crystals approaches that given by the macroscopic surface energy and tension. The rate of convergence to this asymptotic limit will be discussed. Although the vibrational spectrum converges slowly, the first moment of the spectrum converges rapidly to the bulk crystal value. Approximate analytical formulas have been derived which aid in understanding the competing roles of electrostatic, repulsive, and polarization interactions in determining the equilibriuim surface energy and distortions in ionic clusters and microcrystals.