A steady-state study of the nonequilibrium properties of realistic materials: Application of the mixed-configuration approximation

Abstract: We present the mixed-configuration approximation (MCA) based on the auxiliary master equation approach impurity solver to study multiorbital correlated systems under equilibrium and nonequilibrium conditions within dynamical mean-field theory (DMFT). We benchmark the method for bulk and layered SrVO$_3$ in equilibrium and apply it to a prototypical nonequilibrium geometry in which a voltage bias is applied perpendicular to the layer via reservoirs held at different chemical potentials. For bulk SrVO$_3$, MCA reproduces the metallic state at moderate interaction strengths, but it overestimates the weight of the lower band relative to quantum Monte Carlo (QMC) and fork tensor product state (FTPS) solvers. With respect to QMC and FTPS, MCA yields an earlier metal-to-insulator transition as the electron-electron interaction is increased. In layered SrVO$_3$ at equilibrium, MCA partially captures the orbital polarization in favor of the in-plane $xy$ orbital, although not as strong as in the DMFT-converged results obtained with QMC. However, when performing a one-shot impurity calculation initialized with the DFMT-QMC results, MCA yields orbital occupations which show a stronger charge polarization in favor of orbital $xy$. This suggests that our approach can be used to study multiorbital impurity problems when the focus is to assess properties without performing the full DMFT self-consistent loop. Finally, under applied bias, we observe a pronounced redistribution of orbital occupations, demonstrating that the method captures bias-driven orbital charge transfer in realistic materials in nonequilibrium conditions.