Eur. Phys. J. B 68, 309-315 (2009)
https://doi.org/10.1140/epjb/e2008-00399-x

Role of the attractive intersite interaction in the extended Hubbard model

¹ Dipartimento di Fisica “E. R. Caianiello”, Unità CNISM di Salerno, Università degli Studi di Salerno, Via S. Allende, 84081 Baronissi (SA), Italy
² Dipartimento di Fisica and Sezione I.N.F.N., Università degli Studi di Perugia, Via A. Pascoli, 06123 Perugia, Italy
³ Unità CNISM di Salerno, Dipartimento di Fisica “E. R. Caianiello”, Università degli Studi di Salerno, Via S. Allende, 84081 Baronissi (SA), Italy

Corresponding author: ^a naddeo@sa.infn.it

Received: 14 July 2008
Revised: 16 September 2008
Published online: 30 October 2008

Abstract

We consider the extended Hubbard model in the atomic limit on a Bethe lattice with coordination number z. By using the equations of motion formalism, the model is exactly solved for both attractive and repulsive intersite potential V. By focusing on the case of negative V, i.e., attractive intersite interaction, we study the phase diagram at finite temperature and find, for various values of the filling and of the on-site coupling U, a phase transition towards a state with phase separation. We determine the critical temperature as a function of the relevant parameters, U/|V|, n and z and we find a reentrant behavior in the plane (U/|V|, T). Finally, several thermodynamic properties are investigated near criticality.