Melting of Aluminum Cluster Cations with 31−48 Atoms: Experiment and Theory

Abstract

Heat capacities have been measured as a function of temperature for aluminum clusters with 31−48 atoms, complimenting previous measurements for larger clusters. Peaks in the heat capacities (due to the latent heat) indicate melting transitions. Large size-dependent fluctuations in the melting temperatures are found in the 31−48 atom size regime, with the lowest melting temperature differing from the highest by close to 400 K. There are also large variations in the latent heats; some clusters show prominent peaks in their heat capacities, whereas for others the peak is virtually absent. A first effort is made to explain the main features of these results by investigating the geometries of the clusters using first principles density functional methods. It appears that clusters that show strong first-order phase transitions have geometries with more uniform bonding (i.e., more similar bond energies and bond lengths) than clusters that lack a strong first-order phase transition. The variation in the melting t...