CONVERGENCE BEHAVIOR OF MANY-BODY PERTURBATION-THEORY WITH LATTICE SUMMATIONS IN POLYMERS

The convergence behavior of many-body perturbation theory (MBPT) with lattice summations directly reflects the spatial property of electron correlation in extended systems. A knowledge of such properties is ess ential for both theory and numerical calculations. It is shown solely from theory that the second-order MBPT contribution to the total energ y per unit cell in polymers converges with lattice size N as 1/N-3 whi le the second-order MBPT contribution to the band energy converges as 1/N-2. These convergence behaviors are demonstrated numerically for po lyacetylene.