Improved effective vertices in the multi-orbital Two-Particle Self-Consistent method from Dynamical Mean-Field Theory

TL;DR

This paper develops an improved multi-orbital TPSC method integrated with DMFT to accurately capture local and non-local correlations, extending applicability to strongly correlated systems and enhancing the calculation of effective vertices.

Contribution

It introduces a novel multi-orbital TPSC approach using DMFT-derived vertices and self-energy, improving accuracy and applicability in strongly correlated regimes.

Findings

More accurate local vertices in weakly correlated regimes.

Ability to access stronger correlated systems previously out of reach.

Significant improvement in local spectral functions in strongly correlated regimes.

Abstract

In this work we present a multi-orbital form of the Two-Particle Self-Consistent approach (TPSC), here the effective local and static irreducible interaction vertices are determined by means of the Dynamical Mean-Field Theory (DMFT). This approach replaces the approximate ansatz equations for the double occupations $\langle n^{}_{\alpha,\sigma}n^{}_{\beta,\sigma'}\rangle$ by sampling them directly for the same model using DMFT. Compared to the usual Hartree-Fock like ansatz, this leads to more accurate local vertices in the weakly correlated regime, and provides access to stronger correlated systems that were previously out of reach. This approach is extended by replacing the local component of the TPSC self-energy by the DMFT impurity self-energy, which results in an improved self-energy that incorporates strong local correlations but retains a non-trivial momentum-dependence. We find that this combination of TPSC and DMFT provides a significant improvement over the multi-orbital formulation of multi-orbital TPSC, as it allows to determine the components of the spin vertex without artificial symmetry assumptions, and opens the possibility to include the transversal particle-hole channel. The new approach is also able to remove unphysical divergences in the charge vertices in TPSC. We find a general trend that lower temperatures can be accessed in the calculation. Benchmarking single-particle quantities such as the local spectral function with other many-body methods we find significant improvement in the more strongly correlated regime.