Model for FeSi, a strongly correlated insulator

TL;DR

This paper discusses a model for FeSi, a strongly correlated insulator, comparing different perturbation theory methods and clarifying their applicability and limitations.

Contribution

The paper provides a detailed comparison between the second order perturbation theory and the iterated perturbation theory for modeling FeSi, highlighting their differences and regimes of validity.

Findings

The second order perturbation theory has limitations at large U values.

The IPT method performs well in the large U limit.

Our conclusions are consistent despite methodological differences.

Abstract

Revised to reflect the differences between the second order perturbation theory method developed by Scheitzer and Czycholl, and followed by us, and the iterated perturbation theory (IPT)of Georges and Kotliar, et al. Because of our domain of interest, this does not materially change our conclusions, but it is important to realize that the method used here fails in the limit of large $U$, where IPT has had good results.