First-principles DFT+GW study of oxygen vacancies in rutile TiO2

TL;DR

This study uses advanced first-principles DFT+GW calculations to analyze oxygen vacancies in rutile TiO2, revealing their charge states, defect levels, and stability depending on Fermi level position.

Contribution

It introduces a combined DFT+GW approach with electrostatic corrections to accurately characterize defect states in TiO2.

Findings

Oxygen vacancies are negative U defects.

+2 charge state is stable below 2.8 eV Fermi level.

Neutral charge state is stable above 2.8 eV Fermi level.

Abstract

We perform first-principles calculations of the quasiparticle defect states, charge transition levels, and formation energies of oxygen vacancies in rutile titanium dioxide. The calculations are done within the recently developed combined DFT+GW formalism, including the necessary electrostatic corrections for the supercells with charged defects. We find the oxygen vacancy to be a negative U defect, where U is the defect electron addition energy. For the values of Fermi level below 2.8 eV (relative to the valence band maximum) we find the +2 charge state of the vacancy to be the most stable, while above 2.8 eV we find that the neutral charge state is the most stable.