Parquet-like equations for the Hedin three-leg vertex

TL;DR

This paper introduces a new set of equations, inspired by parquet and Hedin formalisms, that efficiently sum certain diagram classes in correlated electron systems, avoiding computationally expensive vertex function calculations.

Contribution

It derives a closed set of equations for the Hedin three-leg vertex using the SBE decomposition, simplifying parquet-based calculations in many-body problems.

Findings

Demonstrated convergence for the Anderson impurity model

Circumvents calculation of four-point vertex functions

Avoids inversion of Bethe-Salpeter equations

Abstract

Taking the competition and the mutual screening of various bosonic fluctuations in correlated electron systems into account requires an unbiased approach to the many-body problem. One such approach is the self-consistent solution of the parquet equations, whose numerical treatment in lattice systems is however prohibitively expensive. In a recent article it was shown that there exists an alternative to the parquet decomposition of the four-point vertex function, which classifies the vertex diagrams according to the principle of single-boson exchange (SBE) [F. Krien, A. Valli, and M. Capone, arXiv:1907.03581 (2019)]. Here we show that the SBE decomposition leads to a closed set of equations for the Hedin three-leg vertex, the polarization, and the electronic self-energy, which sums self-consistently the diagrams of the Maki-Thompson type. This circumvents the calculation of four-point vertex functions and the inversion of the Bethe-Salpeter equations, which are the two major bottlenecks of the parquet equations. The convergence of the calculation scheme starting from a fully irreducible vertex is demonstrated for the Anderson impurity model.