Thermodynamics of Pseudospin-Electron Model in the U=0 Limit

Thermodynamics of a pseudospin-electron model without correlations is investigated. The correlation functions, the mean values of pseudospin and particle number, as well as the thermodynamic potential are calculated. The calculation is performed by a diagrammatic method in the mean field approximation. Single-particle Green functions are taken in the Hubbard-I approximation. The numerical research shows that an interaction between the electron and pseudospin subsystems leads in the $\mu={}$const regime to the possibility of the first order phase transition at the temperature change with the jump of the pseudospin mean value $<S^z>$ and reconstruction of the electron spectrum. In the regime $n={}$const, an instability with respect to phase separation in the electron subsystem can take place for certain values of the model parameters.