Investigation into the inadequacy of cRPA in reproducing screening in strongly correlated systems

TL;DR

This study reveals that cRPA often overestimates screening effects in strongly correlated systems, leading to inaccuracies in effective models, and proposes a new local polarization-based method for better screening analysis.

Contribution

The paper demonstrates the limitations of cRPA in reproducing spectral properties and introduces a local polarization approach that more accurately captures screening in correlated systems.

Findings

cRPA overestimates Hubbard U screening in DMFT models

The new local polarization method better reproduces spectral features

RPA's fully screened interaction W is overscreened and misses local screening signatures

Abstract

The accuracy of the constrained random phase approximation(cRPA) method is examined in multi-orbital Hubbard models containing all possible on-site density-density interactions. Using DMFT, we show that the effective model constructed using cRPA fails to reproduce the spectral properties of the original full model in a wide parameter range. By comparing quantities such as the density of states and quasiparticle residues of the full and the effective models, we show that cRPA systematically overestimates the screening of Hubbard U for DMFT impurity solvers. We instead propose a new method to investigate the screening mechanism in the system using the local polarization, which is highly successful in reproducing spectra and also shows that the true screening is far less than that predicted by RPA. Furthermore, we compare the fully screened interaction $W$ given by RPA and our new method and show that the RPA $W$ is also overscreened and misses the signatures of local screening, which are clearly present in our new method.