Relationship between band populations and band structure in the three-band Hubbard model

We study the two-dimensional three-band Hubbard model by means of a four-pole approximation within the Composite Operator Method framework. The model has been solved by considering as basic composite field a four-component spinor field, which includes the p field, the two Hubbard operators for the d field, and a composite operator describing the p field dressed by the spin excitations of the d field. This solution correctly reproduces many results of numerical simulations. In this manuscript, we investigate the relationship between p-and d- populations and the band structure of the model, by varying the on-site potential, the charge-transfer gap, the doping and the hopping integral between the p orbitals.