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  • Open Access

Extension of the iterated perturbation theory at arbitrary fillings to nonequilibrium steady states

Tommaso Maria Mazzocchi* and Enrico Arrigoni†

  • *Contact author: mazzocchi@tugraz.at
  • †Contact author: arrigoni@tugraz.at
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Phys. Rev. B 114, 175122 – Published 16 September, 2026

DOI: https://doi.org/10.1103/lwg4-6tq8

Abstract

We extend the Kajueter-Kotliar [Phys. Rev. Lett. 77, 131 (1996)] iterated perturbation theory (KK-IPT) away from half-filling to nonequilibrium steady states. We benchmark the resulting nonequilibrium KK-IPT approach against the auxiliary master equation approach (AMEA), whose accuracy is controlled in and out of equilibrium. As expected, in equilibrium, KK-IPT reproduces the AMEA results for different fillings with high accuracy at the level of both spectral properties and electron densities. Out of equilibrium, we study quantum transport across a correlated impurity and compute the differential conductance and spectral functions. We find very good agreement between nonequilibrium KK-IPT and AMEA in the parameter regime where the latter is reliable, in particular at moderate temperatures and biases. Although a controlled benchmark is not available in the low-temperature, low-bias regime, where AMEA becomes less reliable, we show that this nonequilibrium KK-IPT impurity solver satisfies the exact spectral sum rules for the first and second moments to high accuracy throughout the entire parameter range studied. These results support nonequilibrium KK-IPT as an approximate description of nonequilibrium steady states away from half-filling. At the same time, comparing against AMEA the double occupancy obtained from the nonequilibrium Galitskii-Migdal expression for the interaction energy shows that the deviation from AMEA remains small near half-filling for moderate and large values of the bias, but grows markedly away from half-filling, delineating the regime in which the method can be trusted quantitatively rather than merely qualitatively.

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Phys. Rev. B 114, 175122– Published 16 September, 2026
  • Received 17 April 2026
  • Revised 28 July 2026
  • Accepted 31 August 2026
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