Melting and evaporation transitions in small Al clusters: canonical Monte-Carlo simulations

摘要

A dimer of bound atoms cannot melt, only dissociate. Bulk metals show a welldefined first order transition between their solid and liquid phases. Theappearance of the melting transition is explored for increasing clusters sizesvia the signatures in the specific heat and the root mean square of the bondlengths $\delta_{\rm B}$ (Berry parameter) by means of Monte-Carlo simulationsof Al clusters modelled by Gupta potentials. Clear signatures of a meltingtransition appear for $N\sim 6$ atoms. Closed-shell effects are shown forclusters with up to 56 atoms. The melting transition is compared in detail withthe dissociation transition, which induces a second and possibly much largerlocal maximum in the specific heat at higher temperatures. Larger clusters areshown to fragment into dimers and trimers, which in turn dissociate at highertemperatures.