Cumulant expansion for the p–d model: density of states and hole occupation

Abstract

We propose a nonstandard perturbative solution of the p - d model, based on a generalized cumulant expansion. Using a temperature dependent Green's functions formalism, the behaviour of the density of states and the hole occupation number is investigated in the charge-transfer and in the Mott-Hubbard regime, to describe realistic systems with CuO₂ sheets. A comparison with different analytic and numerical methods is also discussed.