Ions in liquid metal clusters

Abstract

represent the phase transition as a transition between cluster configurational states or sets thereof; each configurational state corresponds to a local minimum of the potential energy surface (PES) of this system as a function of atomic coordinates; typically, the cluster's PES is characterized by many local minima. One can relate the cluster's solid and liquid states directly to one or some combination of configurational states. According to the definition of the liquid aggregate state, one or several cluster atoms may move about the cluster on a time scale short compared with that in which atoms remain "in their knots' in the solid aggregate state.Evidently, the global minimum of the PES corresponds to the most stable solid form of the cluster; other local minima may also act as metastable solid forms. Our goal here is to analyze the nature of the liquid aggregate state of clusters. To understand the nature of the phase transition to this state in clusters, we consider clusters consisting of 13 atoms. Indeed, 13 is the lowest magic number of atoms for many clusters, for which the first icosahedral shell is completed. Of course, some kinds of 13-atom clusters have other structures, and there are even conflicting results from simulations regarding which structure is the global minimum for certain kinds of clusters, such as Au 13 [1-3]; different computational methods sometimes give different results. However, one can safely generalize by recognizing that many kinds of clusters have several low-lying, locally stable structures with similar energies.Configurational excitation is characterized by an energy higher than that of the global minimum, which, for some kinds of clusters, this means with energy above the structure with a maximum number of nearest neighbors. For many clusters, this is the lowest-energy solid state and may be separated from the first excited configurational state by a sizeable energy gap. This simplifies the analysis and allows Abstract From the results of computer simulations, especially of 13-atom metal clusters by molecular dynamics, we derive a theory of the solid-liquid phase transition in metal clusters that connects to the jellium model. We analyze the nature of the ion's behavior in liquid clusters. As a result, we find a dynamical coexistence among the cluster's configurational states create the liquid aggregate state of this cluster. It follows from the entropy analysis that motions of the ions in liquid metal clusters explore a selective set of ion configurations, rather than following independent motions in a self-consistent cluster field.