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Mixed-configuration approximation for multiorbital systems out of equilibrium

Tommaso Maria Mazzocchi*, Daniel Werner, Markus Aichhorn, and Enrico Arrigoni†

  • *Contact author: mazzocchi@tugraz.at
  • †Contact author: arrigoni@tugraz.at
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Phys. Rev. B 112, 155127 – Published 10 October, 2025

DOI: https://doi.org/10.1103/j3c8-cy15

Abstract

We propose a mixed-configuration approximation based on single-band impurity solvers to efficiently study nonequilibrium multiorbital systems at moderate computational cost. In this work, we merge the approach with the so-called auxiliary master equation approach. As a benchmark, we first show that our approach reproduces the results of quantum Monte Carlo (QMC) for two-orbital impurity models at equilibrium with overall good accuracy, especially for nondegenerate orbitals. We then use our approach as an impurity solver for dynamical mean-field theory (DMFT) to address the case of a two-orbital, realistic layered structure, recovering the strong crystal-field-driven charge polarization observed by solving the DMFT self-consistent cycle with QMC, albeit slightly reduced. Finally, we address a prototype nonequilibrium setup by sandwiching this layer between metallic contacts subject to a bias voltage described by different chemical potentials. This simplified model demonstrates our method's potential to access nonequilibrium steady-state behavior of multiorbital, realistic materials. These findings provide a first-step basis for theoretical studies of nonequilibrium properties of multiorbital compounds directly in the real frequency domain.

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Phys. Rev. B 112, 155127– Published 10 October, 2025
  • Received 15 July 2025
  • Revised 26 September 2025
  • Accepted 30 September 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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