Modeling Excited States of Point Defects in Materials from Many-Body Perturbation Theory

Point defects are often naturally present in materials or incorporated intentionally to achieve new functionality and can dominate the optoelectronic properties of materials. To better control their impact, it is necessary to understand how the presence of a specific defect results in new electronic excitations. To this end, first-principles calculations have provided important insight into the energetics associated with point defects in materials, such as trap state energies, absorption energies, charge transition levels, and formation energies. In this review article, we provide an overview of many-body perturbation theory (MBPT) studies aimed at predicting excited-state energies in defective materials with quantitative accuracy. While first-principles density functional theory (DFT) has been applied extensively to these material systems, MBPT provides a greater degree of accuracy in electron–electron interactions that may be required in some cases at the cost of greater computational complexity. We show that MBPT predicts quantitatively accurate energies when compared with experiment in limited cases for which it has been tested. Additionally, we discuss benchmarks against DFT and limitations due to common approximations, including the dependence on the DFT starting point and exclusion of electron–phonon interactions. Lastly, we discuss new insight provided by MBPT for materials with deep localized defect states and strong excitonic effects.