Defect Energy Levels in Density Functional Calculations: Alignment and Band Gap Problem

TL;DR

This study compares defect energy levels calculated with different density functional schemes, showing how they shift with band gap corrections and providing guidelines for aligning theoretical and experimental defect levels.

Contribution

It demonstrates the relationship between defect level calculations and band gap corrections in density functional theory, offering a method for better alignment with experimental data.

Findings

Defect levels shift up to 0.2 eV when aligning different schemes.

Systematic deviations increase with defect wave function extent.

A guideline for comparing calculated and experimental defect levels is provided.

Abstract

For materials of varying band gap, we compare energy levels of atomically localized defects calculated within a semilocal and a hybrid density-functional scheme. Since the latter scheme partially relieves the band gap problem, our study describes how calculated defect levels shift when the band gap approaches the experimental value. When suitably aligned, defect levels obtained from total-energy differences correspond closely, showing average shifts of at most 0.2 eV irrespective of band gap. Systematic deviations from ideal alignment increase with the extent of the defect wave function. A guideline for comparing calculated and experimental defect levels is provided.