Causality violations in cluster GW+DMFT: Exact Lehmann moments and the necessity of non-local vertex corrections
The study investigates whether combining GW with DMFT fixes causality violations in frustrated clusters. While GW+DMFT restores causality for simple systems like dimers, it fails for structures like three-site rings because local self-energy corrections are insufficient. The failure is traced to uncorrected non-local vertex correlations.