The thermodynamical limit of strongly correlated systems obtained from small-size-cluster calculations

We study the properties of strongly correlated systems, calculating the sel f-energy of the electronic propagator of small-size clusters. We focus our attention on the one-dimensional Hubbard model. It is shown that for adequa te sizes and boundary conditions, the self-energy of such a small cluster p ossesses the correct singular behaviour in the vicinity of the Fermi level for all values of the intra-atomic electron-electron interaction parameter U. The charge-transfer gap and other physical properties of the system are obtained at the thermodynamic limit. The survival of a single-pole singular ity at w = 0 for the infinite-system self-energy constitutes a criterion fo r establishing whether the system is an insulator or a metal.