The broken-pair model versus the quasi-particle scheme: Two different formalisms?

Abstract

The particle-number conserving Broken-Pair Model (BPM) and the Quasi-Particle Scheme (QPS) are shown to be nothing but two aspects of the same formalism. As a consequence, the old problem of the number-projection becomes elementary and BPM is algebraically as simple as QPS. Furthermore, owing to the existence of simple recursion formulas, BPM is also numerically as tractable as QPS.