THE ELECTRONIC-STRUCTURE OF THE COPPER-OXIDE PLANE WITHIN THE GREEN-FUNCTIONS PROJECTION METHOD

The projection method for two-time Green functions is used to derive a self-consistent set of equations for the spectrum of the two-dimensional Emery model with infinite copper correlation. In the relevant parameter region near the filling n = 1 a charge-transfer gap is found, but in difference to the Gutzwiller approximation a finite bandwidth occurs at the transition point. The critical DELTA-c = epsilon-p - epsilon-d at which the transition to metallic behaviour occurs is found to be approximately DELTA-c = 2t.