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

TL;DR

This paper introduces the mixed-configuration approximation (MCA) within DMFT to study nonequilibrium properties of multiorbital materials, benchmarking it against established methods and demonstrating its ability to capture bias-driven charge transfer.

Contribution

The paper develops and benchmarks the MCA method for nonequilibrium multiorbital systems within DMFT, showing its effectiveness and limitations compared to QMC and FTPS.

Findings

MCA reproduces the metallic state in bulk SrVO₃ at moderate interactions.

MCA overestimates the lower band weight compared to QMC and FTPS.

Under bias, MCA captures orbital charge redistribution in realistic materials.

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.