Hubbard interactions in iron-based pnictides and chalcogenides: Slater parametrization, screening channels and frequency dependence

TL;DR

This paper calculates and analyzes the frequency-dependent on-site electronic interactions in various iron-based superconductors using first-principles methods, highlighting the importance of screening channels and the validity of atomic-like parametrizations.

Contribution

It provides a detailed first-principles analysis of the frequency-dependent interactions and evaluates the accuracy of Slater parametrization across different iron pnictides and chalcogenides.

Findings

Atomic-like parametrization is accurate for ionic-like Fe-Se but less so for covalent Fe-As compounds.

Ligand screening is less dominant in pnictides compared to oxides.

The frequency dependence of interactions in pnictides involves multiple modes beyond a single plasmon.

Abstract

We calculate the strength of the frequency-dependent on-site electronic interactions in the iron pnictides LaFeAsO, BaFe2As2, BaRu2As2, and LiFeAs and the chalcogenide FeSe from first principles within the constrained random phase approximation. We discuss the accuracy of an atomic-like parametrization of the two-index density-density interaction matrices based on the calculation of an optimal set of three independent Slater integrals, assuming that the angular part of the Fe-d localized orbitals can be described within spherical harmonics as for isolated Fe atoms. We show that its quality depends on the ligand-metal bonding character rather than on the dimensionality of the lattice: it is excellent for ionic-like Fe-Se (FeSe) chalcogenides and a more severe approximation for more covalent Fe-As (LaFeAsO, BaFe2As2) pnictides. We furthermore analyze the relative importance of different screening channels, with similar conclusions for the different pnictides but a somewhat different picture for the benchmark oxide SrVO3: the ligand channel does not appear to be dominant in the pnictides, while oxygen screening is the most important process in the oxide. Finally, we analyze the frequency dependence of the interaction. In contrast to simple oxides, in iron pnictides its functional form cannot be simply modeled by a single plasmon, and the actual density of modes enters the construction of an effective Hamiltonian determining the low-energy properties.