Entropy behavior in cluster melting.

We analyze the configurational excitation of a cluster for both a microcanonical and a canonical ensemble of atoms and apply this analysis to the Lennard-Jones cluster of 13 atoms. Dividing the cluster excitations into configurational and thermal classes, we evaluate the anharmonicity coefficient of atomic vibrations and the entropy jump as a function of temperature on the basis of computer simulations of the Lennard-Jones 13-atom cluster as a canonical and a microcanonical ensemble of atoms. This analysis shows the role of anharmonicity of atomic vibrations and exhibits the importance of the temperature dependence of the entropy jump in the range of phase coexistence for cluster thermodynamics.