Method for calculating the electronic structure of correlated materials from a truly first-principles LDA+U scheme

TL;DR

This paper introduces a self-consistent, first-principles LDA+U method for calculating the electronic structure of correlated materials, improving accuracy in bandgap and exchange splitting predictions.

Contribution

It develops a stable, iterative approach to determine the Hubbard U parameter from first-principles within the LDA+U framework.

Findings

Improved bandgap prediction in NiO

Enhanced f-band exchange spin-splitting in Gd

Method remains stable and convergent

Abstract

We present a method for calculating the electronic structure of correlated materials based on a truly first-principles LDA+U scheme. Recently we suggested how to calculate U from first-principles, using a method which we named constrained RPA (cRPA). The input is simply the Kohn-Sham eigenfunctions and eigenvalues obtained within the LDA. In our proposed self-consistent LDA+U scheme, we calculate the LDA+U eigenfunctions and eigenvalues and use these to extract U. The updated U is then used in the next iteration to obtain a new set of eigenfunctions and eigenvalues and the iteration is continued until convergence is achieved. The most significant result is that our numerical approach is indeed stable: it is possible to find the effective exchange and correlation interaction matrix in a self-consistent way, resulting in a significant improvement over the LDA results, regarding both the bandgap in NiO and the f-band exchange spin-splitting in Gd, but some discrepancies still remain.