Ab initio calculations of quasiparticle band structure in correlated systems: LDA++ approach

TL;DR

This paper presents a comprehensive ab initio framework for calculating quasiparticle band structures in correlated electron systems, integrating various many-body approaches tailored to different interaction regimes.

Contribution

It introduces a unified method combining Hubbard-I, DMFT, and FLEX approaches for realistic electronic structure calculations in correlated materials.

Findings

Successful application to TmSe and NiO demonstrating the method's versatility.

Extension of existing models to multiband, realistic systems.

Comparison of different regimes shows the method's adaptability.

Abstract

We discuss a general approach to a realistic theory of the electronic structure in materials containing correlated d- or f- electrons. The main feature of this approach is the taking into account the energy dependence of the electron self-energy with the momentum dependence being neglected (local approximation). In the case of strong interactions (U/W>>1 - rare-earth system) the Hubbard-I approach is the most suitable. Starting from an exact atomic Green function with the constrained density matrix the band structure problem is formulated as the functional problem on Nmm' for f-electrons and the standard LDA-functional for delocalized electrons. In the case of moderate correlations (U/W=1 metal-insulator regime) we start from the dynamical mean field iterative perturbation scheme (IPS) of G. Kotliar et. al. and also make use of our multiband atomic Green function. Finally for the weak interactions (U/W<1 -transition metals) the self-consistent diagrammatic fluctuation- exchange (FLEX)-approach of N. Bickers and D. Scalapino is generalized to the realistic multiband case. We presents two-band, two-dimensional model calculations for all three regimes. A realistic calculation in Hubbard-I scheme with the exact solution of the on-site multielectron problem for f(d)- shells was performed for mixed-valence 4f compound TmSe, and for the classical Mott insulator NiO.