Ab-initio Downfolding for SrVO₃from Quantum Monte Carlo

When deriving interacting Model Hamiltonians for real materials, the choice of basis in the downfolded Hilbert space is critical for the accuracy of the resultant model. Typically, one starts by choosing a subset of density functional theory (DFT) orbitals, followed by evaluating screened Coulomb interactions within the chosen correlated subspace using a diagrammatic summation. However, for strongly correlated systems, the basis given by DFT can sometimes be biased, and the summation is almost always truncated; therefore, it is preferable to start from more accurate many-body calculations and bypass the basis dependence when deriving models.

In this work, we present an alternative approach that starts with real-space quantum Monte Carlo (QMC) calculations of the neutral ground state and a few low-energy charged excited states in SrVO₃. The optimal interacting model is obtained by minimizing the spectrum residual after directly matching the QMC states with the eigenstates of the proposed models. Our results demonstrate the potential of QMC to enable reliable predictions in strongly correlated materials by producing more accurate interacting models as inputs for quantum embedding theories.