ASSESSMENT OF THE GW APPROXIMATION USING HUBBARD CHAINS

We investigate the performance of the GW approximation by comparison t o exact results for small model systems. The role of the chemical pote ntials in Dyson's equation as well as the consequences of numerical re sonance broadening are examined, and we show how a proper treatment ca n improve computational implementations of many-body perturbation theo ry in general. Exchange-only and GW-calculations are performed over a wide range of fractional band fillings and correlation strengths. We t hus identify the physical situations where these schemes are applicabl e.