Quantum embedding for strongly correlated defects in PAW calculations from the algorithmic inversion method

Novel quantum embedding methods are needed to be able to address the strong electronic correlations present in defect states in materials. Here, we embed high-level wavefunction methods (CI or CASSCF) in a density-functional bath, to be able to describe multi-reference correlations within the defect. This hybrid approach allows for an accurate treatment of the static correlations that are typically challenging for DFT. The all-electron DFT wavefunction is reconstructed using the projector augmented-wave (PAW) formalism, providing accurate Coulomb integrals and an improved representation of multi-reference effects. Crucially, the approach leverages a Green’s function formulation where the embedding takes the form of a sum-over-pole propagator obtained from the algorithmic-inversion method [1]. We showcase the accuracy of the approach on small molecules, with the goal of applying it to the study of defects, impurities, or correlated (periodic) crystals.

[1] T. Chiarotti, A. Ferretti, and N. Marzari, Phys. Rev. Research 6, L032023 (2024)