Color centers in NaCl by hybrid functionals

TL;DR

This paper investigates the electronic structure and transition energies of Cl vacancies in NaCl using hybrid density functionals, highlighting improvements and limitations in modeling defect states and optical properties.

Contribution

It demonstrates that hybrid functionals can better reproduce experimental band gaps and lattice relaxations but still face challenges in accurately predicting ionization energies and defect transition energies.

Findings

Hybrid functionals recover the band gap problem.

Better lattice relaxation modeling with hybrid functionals.

Quantitative agreement with experimental transition energies remains challenging.

Abstract

We present in this work the electronic structure and transition energies (both thermodynamic and optical) of Cl vacancies in NaCl by hybrid density functionals. The underestimated transition energies by the semi-local functional inherited from the band gap problem are recovered by the PBE0 hybrid functional through the non-local exact exchange, whose amount is adjusted to reproduce the experimental band gap. The hybrid functional also gives a better account of the lattice relaxation for the defect systems arising from the reduced self-interaction. On the other hand, the quantitative agreement with experimental vertical transition energy cannot be achieved with hybrid functionals due to the inaccurate descriptions of the ionization energies of the localized defect and the positions of the band edges.