Size-consistency aspects and physical interpretation of many-body green's function calculations on extended chains

A general proof of the size consistency of the many-body Green’s-function and the related Rayleigh-Schrödinger perturbation theory methods is provided, on the basis of the linked-cluster theorem, for infinite polymer systems. It is assessed by means of calculations of the ionization potentials, and their corresponding pole strengths, on increasing-size model oligomers achieved using the equation-of-motion–algebraic superoperator approach. The orbital picture for the ionization process is shown to be partially preserved in infinite systems. The dependence of the correlation and relaxation effects with the size of the system and the inner character of the ionized orbitals, is interpreted within the framework of the band-structure formalism. The hierarchy observed among the many-body corrections obtained at several levels of approximation used to expand the one-particle propagator are also explained by diagrammatic considerations.