Nonconcave entropies from generalized canonical ensembles

Marius Costeniuc, Richard S. Ellis, and Hugo Touchette

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Submission date: 14. Sep. 2006
Pages: 7
published in: Physical review / E, 74 (2006), art-no. 010105 
DOI number (of the published article): 10.1103/PhysRevE.74.010105
Bibtex
PACS-Numbers: 05.20.-y, 05.20.Gg, 64.40.-i
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Abstract:
It is well known that the entropy of the microcanonical ensemble cannot be calculated as the Legendre transform of the canonical free energy when the entropy is nonconcave. To circumvent this problem, a generalization of the canonical ensemble that allows for the calculation of nonconcave entropies was recently proposed. Here, we study the mean-field Curie-Weiss-Potts spin model and show, by direct calculations, that the nonconcave entropy of this model can be obtained by using a specific instance of the generalized canonical ensemble known as the Gaussian ensemble.