Phase diagrams of half-filled 1D and 2D extended Hubbard model within COM

The half-filled extended Hubbard model, in one and two dimensions, is studied by means of the two-pole approximation within the Composite Operator Method with the aim of improving the possibilities to describe some of the experimental features observed for quasi-1D organic superconductors and Cu–O planes of cuprates. The phase diagrams (T–V and V–U) are analyzed with respect to the paramagnetic metal—paramagnetic insulator—charge ordered phase transitions. The relevant features of the diagrams (rank of the phase transitions, critical points, reentrant behavior) are discussed in detail.