# Limitations of the DFT-1/2 method for covalent semiconductors and transition-metal oxides

## TL;DR

This paper critically examines the limitations of the DFT-1/2 method in accurately predicting band gaps for covalent semiconductors and transition-metal oxides, emphasizing the importance of orbital separation for improved results.

## Contribution

It provides a detailed analysis of the DFT-1/2 method's limitations for specific material classes and clarifies the conditions needed for its effective application.

## Key findings

- DFT-1/2 can be inaccurate for covalent semiconductors and transition-metal oxides.
- Effective band gap correction requires spatial separation of valence and conduction orbitals.
- Caution is advised when applying DFT-1/2 to complex materials.

## Abstract

The DFT-1/2 method in density functional theory [L. G. Ferreira et al., Phys. Rev. B 78, 125116 (2008)] aims to provide accurate band gaps at the computational cost of semilocal calculations. The method has shown promise in a large number of cases, however some of its limitations or ambiguities on how to apply it to covalent semiconductors have been pointed out recently [K.-H. Xue et al., Comput. Mater. Science 153, 493 (2018)]. In this work, we investigate in detail some of the problems of the DFT-1/2 method with a focus on two classes of materials: covalently bonded semiconductors and transition-metal oxides. We argue for caution in the application of DFT-1/2 to these materials, and the condition to get an improved band gap is a spatial separation of the orbitals at the valence band maximum and conduction band minimum.