Core-melted clusters

The possibility of the existence of a core-melted cluster is investigated. To this end, a pair potential is introduced, with the property that the sol id state of the cluster is less dense than the liquid state. With this kind of potential, the cluster exhibits a quite unusual behavior. In addition t o the known states, solid, liquid, and surface-melted, it can also be found in a "dense-liquid" phase (a disordered state appearing at low temperature s), a "core-melted" phase, and a "core-surface-melted" phase. In the core-m elted phase, the external part of the cluster consists of atoms that are vi brating around regular crystalline sites, while the core atoms have much bi gger mobility, sometimes exhibiting a diffusive motion. The phase diagrams for different parameters that enter in the model potential are analyzed.