We present a scalable single-particle framework to treat
electronic
correlation in molecules and materials motivated by Green’s
function theory. We derive a size-extensive Brillouin-Wigner perturbation
theory from the single-particle Green’s function by introducing
the Goldstone self-energy. This new ground state correlation energy,
referred to as Quasi-Particle MP2 theory (QPMP2), avoids the characteristic
divergences present in both second-order Møller–Plesset
perturbation theory and Coupled Cluster Singles and Doubles within
the strongly correlated regime. We show that the exact ground state
energy and properties of the Hubbard dimer are reproduced by QPMP2
and demonstrate the advantages of the approach for larger Hubbard
models where the metal-to-insulator transition is qualitatively reproduced,
contrasting with the complete failure of traditional methods. We apply
this formalism to characteristic strongly correlated molecular systems
and show that QPMP2 provides an efficient, size-consistent regularization
of MP2.