Point defects, including vacancies, interstitials, antisites, and impurity atoms, are ubiquitous in all materials and can have a profound influence on their properties. Density-functional theory (DFT) calculations have proven to be a crucial tool for defect identification and characterization. However, such calculations have fundamental limitations, e.g., for excited electronic states that may have correlated, multireference nature. This motivates the application of many-body methods to treat such cases. However, the large system sizes necessary to treat isolated defects in their bulk host constitutes a challenge for many-body methods because of their computational cost. Recently, quantum embedding approaches, where a small set of states is treated via many-body methods as a correlated active space, while the weakly-correlated bulk is treated with DFT, have shown promise for defects. In this talk, I will describe one such approach, based on Wannierization of defect orbitals and constrained random-phase approximation calculation of screened Coulomb interactions. I will demonstrate that quantitative accuracy can be achieved using the nitrogen-vacancy center in diamond; using carbon-based defects in BN I will show how this method can be used to elucidate the effects of the environment on defect properties; and finally with Fe in III-nitride semiconductors, I will illustrate the promise and potential challenges of the methodology.

Quantum embedding for point defects: Case studies and challenges

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ACS Spring 2023

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