Variational local moment approach: from Kondo effect to Mott transition in correlated electron systems

TL;DR

The paper introduces the variational local moment approach (VLMA) for the Anderson model, providing a unified, conserving, and thermodynamically consistent method to study Kondo effects and Mott transitions in correlated electron systems.

Contribution

VLMA extends the local moment approach by incorporating a variational principle, enabling comprehensive treatment of Fermi, non-Fermi liquid, and local moment regimes.

Findings

VLMA accurately describes various Kondo regimes.

It is a conserving and thermodynamically consistent approximation.

VLMA effectively serves as an impurity solver in dynamical mean-field theory.

Abstract

The variational local moment approach (VLMA) solution of the single impurity Anderson model is presented. It generalizes the local moment approach of Logan et al. by invoking the variational principle to determine the lengths of local moments and orbital occupancies. We show that VLMA is a comprehensive, conserving and thermodynamically consistent approximation and treats both Fermi and non-Fermi liquid regimes as well as local moment phases on equal footing. We tested VLMA on selected problems. We solved the single- and multi-orbital impurity Anderson model in various regions of parameters, where different types of Kondo effects occur. The application of VLMA as an impurity solver of the dynamical mean-field theory, used to solve the multi-orbital Hubbard model, is also addressed.