The effect of the range of the potential on the structure and stability of simple liquids: From clusters to bulk, from sodium to C-60

For systems with sufficiently short-ranged interparticle forces, such as some colloidal systems and perhaps Cao, the liquid phase can be thermodynamically unstable. By analysing the effect of the range of the interatomic forces on the multidimensional potential energy surfaces of bulk material and clusters, a microscopic view of this phenomenon is provided. Structural analysis of the minima on the potential energy surface provides evidence for the polytetrahedral character of the liquid phase, and allows us to examine the evolution of the phase-like forms of clusters to the bulk limit. We find that essentially bulk-like liquid structure can develop in clusters with as few as 55 atoms. The effect of the range of the potential on the thermodynamics is illustrated by a series of simulations of 55-atom clusters. For small clusters bound by long-ranged potentials the lowest energy minimum has an amorphous structure typical of the liquidlike state. This suggests an explanation for the transition from electronic to geometric magic numbers observed in the mass spectra of sodium clusters.