Invitation Only
Talk 1:
Ab initio GW+EDMFT, Part I: Toward Scalable Quantum Embedding
Chia-Nan Yeh, Flatiron Institute
The combination of the GW approximation with extended dynamical mean-field theory, GW+EDMFT, provides a first-principles framework for describing nonlocal screening and strong local correlations simultaneously, with self-consistently determined Coulomb interactions and a well-defined double-counting treatment. Its broader application, however, has been limited by the computational cost of self-consistent, full-frequency GW calculations that go beyond a quasiparticle description, particularly the construction and storage of dynamical two-particle quantities. In this talk, I will discuss how interpolative separable density fitting (ISDF) enables a compact tensor hypercontraction (THC) representation of the Coulomb interaction, thereby yielding a cubic-scaling, full-frequency algorithm for GW calculations. I will conclude with our self-consistent ab initio GW+EDMFT implementation, where this low-scaling GW formulation enables parameter-free quantum embedding calculations for realistic correlated materials.
Talk 2:
Ab initio GW+EDMFT, Part II – From Overscreening to Mott Gaps, self-consistent correlations and screening in Oxides
Francesco Petocchi, Fribourg University
Predictive first‑principles descriptions of correlated solids must treat spectral redistribution and Coulomb screening on equal footing. In common multi‑tier embeddings, the effective interaction is inherited from a fixed mean‑field bandstructure; when correlations reshape low‑energy states, this mismatch can produce overscreening and, in some cases, prevent insulating solutions. Full self‑consistency between the electronic Green’s function and the dynamically screened interaction closes this feedback loop and recovers the experimentally observed behavior. For cubic SrMnO$_3$, self‑consistency removes spurious low‑energy polarization channels and stabilizes a paramagnetic Mott insulator with Hubbard bands and a gap consistent with PES/XAS, capturing the paramagnetic insulating state that previous multi‑tier implementations failed to reproduce. For the negative charge‑transfer metal LaNiO$_3$, the same framework retains a coherent e$_g$ quasiparticle with intermediate mass enhancement while revealing correlation‑induced changes in low‑energy screening and charge fluctuations that are missed in perturbative treatments. The approach yields a consistent interaction without ad hoc inputs or heuristic double‑counting corrections. I conclude with new results for La$_2$CuO$_4$, showing that embedding choices respecting Cu–O covalency and the relevant screening channels are essential to obtain a robust charge‑transfer insulating solution.