Quasiparticle Band Structure and Density Functional Theory: Single-Particle Excitations and Band Gaps in Lattice Models

TL;DR

This paper compares quasiparticle band structures from FEA with DFT and LDA in a model insulator, revealing that LDA overestimates the band gap due to its frequency dependence, challenging conventional views.

Contribution

It provides a detailed comparison of FEA and DFT band structures in a model insulator, highlighting the impact of frequency dependence on band gap estimation.

Findings

FEA and DFT band structures are in good agreement for the model.

LDA overestimates the band gap contrary to conventional wisdom.

The FEA self-energy's frequency dependence is key to understanding the results.

Abstract

We compare the quasiparticle band structure for a model insulator obtained from the fluctuation exchange approximation (FEA) with the eigenvalues of the corresponding density functional theory (DFT) and local density approximation (LDA). The discontinuity in the exchange-correlation potential for this model is small and the FEA and DFT band structures are in good agreement. In contrast to conventional wisdom, the LDA for this model overestimates the size of the band gap. We argue that this is a consequence of an FEA self-energy that is strongly frequency dependent, but essentially local.