Accidental accuracy and formal consistency in GW +BSE: Exact benchmarks and regime-dependent error cancellation
The study investigates why combining GW approximation with Bethe-Salpeter equation (BSE) often yields accurate results despite formal inconsistency between the self-energy and kernel definitions. Using an exact Hubbard dimer benchmark, it shows that accuracy arises from regime-dependent error cancellation rather than hidden formal consistency, providing a diagnostic tool for standard many-body workflows.