Molecular-dynamics study of the binding energy and melting of transition-metal clusters

Effect of Potential Energy Distribution on the Melting of Clusters

“…There has been some controversy concerning the dependence of the simulated thermodynamic properties on the ensemble until the work by Calvo and Labastie [17]. These authors [17] showed that if the sampling of the phase space is accurate enough (a large enough number of MC configurations and MD trajectories), the thermodynamic results are identical in both ensembles because the thermodynamics is determined by the configurational density of states [7,8,17,18].In this Letter, we show that the potential energy distribution of atoms in the clusters can consistently explain many of the important phenomena which occur during phase changes of small clusters, such as the nonmonotonic variation of melting temperature with the size of clusters [3,6,7], the dependence of melting, boiling, and sublimation temperatures on the interatomic potentials [12,13,19], the existence of a surface-melted phase [6,8,11,15,16], and the absence of a premelting peak in heat capacity curves [9,[14][15][16].We have studied the thermodynamic behavior of clusters of metals and nonmetals for the sizes of 12 # n # 34. For the interatomic interactions, we have employed the tight-binding potentials based on the second moment approximation [7,16] for metal clusters (M n , M Ni, Cu, Pd, Ag, Pt, Au, Al, and Pb) and pair potentials for nonmetal clusters.…”

“…In this Letter, we show that the potential energy distribution of atoms in the clusters can consistently explain many of the important phenomena which occur during phase changes of small clusters, such as the nonmonotonic variation of melting temperature with the size of clusters [3,6,7], the dependence of melting, boiling, and sublimation temperatures on the interatomic potentials [12,13,19], the existence of a surface-melted phase [6,8,11,15,16], and the absence of a premelting peak in heat capacity curves [9,[14][15][16].…”

“…Premelting has been attributed to surface melting [8], partial melting [9], orientational disordering in molecular cluster [10], and isomerization [7,11]. It has been observed that clusters can dissipate thermal energy even by boiling [12] and sublimation [13].…”

“…It has been observed that clusters can dissipate thermal energy even by boiling [12] and sublimation [13]. In some clusters, the premelting peak in the heat capacity curve is not observed [9,[14][15][16].…”

“…It has been observed that clusters can dissipate thermal energy even by boiling [12] and sublimation [13]. In some clusters, the premelting peak in the heat capacity curve is not observed [9,[14][15][16].Previously published simulations of cluster melting have used either Monte Carlo (MC) methods at constant temperature (canonical ensemble) or molecular dynamics (MD) at constant energy (microcanonical ensemble). There has been some controversy concerning the dependence of the simulated thermodynamic properties on the ensemble until the work by Calvo and Labastie [17].…”