# Improved strong-coupling perturbation theory of the symmetric Anderson impurity model

## TL;DR

This paper enhances strong-coupling perturbation theory for the symmetric Anderson impurity model by improving self-consistent calculations and resummation techniques, resulting in better predictions of impurity spin responses and antiferromagnetism in the Hubbard model.

## Contribution

It introduces a more accurate self-consistent scheme and updated continued fraction coefficients, advancing the theoretical description of the Anderson impurity model.

## Key findings

- More accurate impurity spin response to magnetic bias.
- Improved description of antiferromagnetism in the Hubbard model.
- Enhanced agreement with expected physical behavior.

## Abstract

In a previous work (N. H. Tong, Phys. Rev. B 92, 165126 (2015)), an equation-of-motion based series expansion formalism was used to do the second-order strong-coupling expansion for the single-particle Green function of the Anderson impurity model. In this paper, we improve this theory in two aspects. We first use a more accurate scheme to self-consistently calculate the averages that appear in G1. In the resummation process, we use updated coefficients for the continued fraction, guided by the formally exact continued fraction from the Mori-Zwanzig theory. These changes lead to more accurate impurity spin response to the magnetic bias of the bath. Combined with the dynamical mean-field theory, our theory gives improved description for the antiferromagnetism of Hubbard model at half filling.