The color center singlet state of oxygen vacancies in TiO$_2$

TL;DR

This study uses advanced quantum chemical methods to clarify the electronic structure of neutral oxygen vacancies in TiO$_2$, revealing a singlet ground state and providing insights into defect properties relevant for catalysis and magnetism.

Contribution

It demonstrates that the ground state of oxygen vacancies in TiO$_2$ is a singlet, resolving previous controversies through high-level electronic structure calculations.

Findings

The ground state of oxygen vacancies in TiO$_2$ is a singlet.

Triplet states are significantly higher in energy (0.6 eV in rutile, 1.4 eV in anatase).

Provides new insights into defect electronic structures using correlated wave function theories.

Abstract

Oxygen vacancies are ubiquitous in TiO$_2$ and play key roles in catalysis and magnetism applications.Despite being extensively investigated, the electronic structure of oxygen vacancies in TiO$_2$ remains controversial both experimentally and theoretically.Here we report a study of a neutral oxygen vacancy in TiO$_2$ using state-of-the-art quantum chemical electronic structure methods.We find that the ground state is a color center singlet state in both the rutile and the anatase phase of TiO$_2$. Specifically, embedded CCSD(T) calculations find, for an oxygen vacancy in rutile, that the lowest triplet state energy is 0.6 eV above the singlet state, and in anatase the triplet state energy is higher by 1.4 eV. Our study provides fresh insights on the electronic structure of the oxygen vacancy in TiO$_2$, clarifying earlier controversies and potentially inspiring future studies of defects with correlated wave function theories.