A two-state model analysis of the melting of sodium clusters: Insights in the enthalpy-entropy compensation

¹ Université de Toulouse, UPS - 118 route de Narbonne, F-31062 Toulouse, France, EU
² CNRS, Laboratoire Collisions Agrégats Réactivité, IRSAMC - F-31062 Toulouse, France, EU
³ LSA, Université de Lyon, UCBL and CNRS, UMR 5180 - 43 Bd. du 11 novembre 1918, Villeurbanne, F-69622, France, EU

^a sebastien.zamith@irsamc.ups-tlse.fr

Received: 28 July 2010
Accepted: 22 September 2010

Abstract

Experimental melting temperatures and associated latent heats of size-selected sodium clusters are analyzed in the frame of a two-state model of melting. The strong variations of these quantities as a function of size make clusters an excellent benchmark for testing speculative ideas about melting. The relation between cohesive energy of clusters and their latent heat of melting is demonstrated, and a correlation between cohesive energy and vibrational frequency in the solid state is found. It is shown that this relation may throw light on the enthalpy-entropy compensation, which is observed in a variety of systems undergoing a first-order phase transition. A relation is established between the Lindemann melting criterion, the variation of the vibrational frequency with the cohesive energy, and the enthalpy-entropy compensation.