Static treatment of dynamic interactions in the single-orbital Anderson impurity model

TL;DR

This paper investigates the validity of using a static interaction approximation in the Anderson impurity model, which is crucial for modeling correlated electron systems, and benchmarks different approaches for mapping dynamic interactions to static ones.

Contribution

It systematically benchmarks static approximations of dynamic interactions in the Anderson impurity model, highlighting regimes where static models are valid or insufficient.

Findings

Static approximation can be valid in certain regimes.

Moment-based approach effectively determines static interaction values.

Dynamic interactions are essential under doping conditions.

Abstract

Correlated electron physics is intrinsically a multiscale problem, since high-energy electronic states screen the interactions between the correlated electrons close to the Fermi level, thereby reducing the magnitude of the interaction strength and dramatically shortening its range. Thus, the handling of screening is an essential ingredient in the first-principles modelling of correlated electron systems. Screening is an intrinsically dynamic process and the corresponding downfolding methods such as the constrained Random Phase Approximation indeed produce a dynamic interaction. However, many low-energy methods require an instantaneous interaction as input, which makes it necessary to map the fully dynamic interaction to an effective instantaneous interaction strength. It is a priori not clear if and when such an effective model can capture the physics of the one with dynamic interaction and how to best perform the mapping. Here, we provide a systematic benchmark relevant to correlated materials, in the form of the Anderson impurity model. Overall, we find that a static approximation can be valid and that the moment-based approach recently proposed by Scott and Booth can be a good tool to find the value of the static interaction. We also identify physical regimes, especially under doping, where an instantaneous interaction cannot capture all of the relevant physics.