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|Type:||Artigo de periódico|
|Title:||CALCULATION OF THE HELMHOLTZ FREE-ENERGY WITH APPROXIMATE GREEN-FUNCTIONS|
|Abstract:||We employ approximate Green's Functions (GF) to obtain the Helmholtz free energy F in a Grand Canonical Ensemble. This study was motivated by the calculation of the total number of electrons N(t) as a function of the chemical potential mu in the Periodic Anderson Model by employing approximate one-electron GF. In this calculation we found that for some parameter values at low T one obtains three values of the chemical potential mu for each N(t) in a small interval of N(t). One of the three states is thermodynamically unstable because N(t) decreases when mu increases, but in the calculation of F by a methods that is based in a thermodynamic relation, this is the most stable of the three. The purpose of this work is to explain this paradox, and we also suggest a variation of the calculation that avoids this difficulty. From geometrical arguments it is clear that this paradox will be always present when N(t) vs. mu has the shape observed in our calculation, independently of the numerical details of the calculation.|
|Editor:||Elsevier Science Bv|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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