Recorded 13 April 2022. Lukas Muechler of Penn State University, Chemistry, presents "Quantum embedding methods for correlated excited states of point defects: Case studies and challenges" at IPAM's Model Reduction in Quantum Mechanics Workshop. Abstract: A quantitative description of the excited electronic states of point defects and impurities is crucial for understanding materials properties, and possible applications of defects in quantum technologies. This is a considerable challenge for computational methods, since KohnSham density-functional theory (DFT) is inherently a ground state theory, while higher level methods are often too computationally expensive for defect systems. Recently, embedding approaches have been applied that treat defect states with many-body methods, while using DFT to describe the bulk host material. In this talk, I will discuss our implementation of such an embedding method, based on Wannierization of defect orbitals and the constrained random-phase approximation. I will review our systematic characterization of the method for three distinct systems with current technological relevance: (i) a carbon dimer replacing a B and N pair in bulk hexagonal BN, (ii) the negatively charged nitrogen-vacancy center in diamond (NV-), and (iii) an Fe impurity on the Al site in wurtzite AlN (FeAl). I will show that the embedding approach for CBCN gives many-body states in agreement with analytical results on the Hubbard dimer model, which allows us to elucidate the effects of the DFT functional and double-counting correction. For the NV- center, our method demonstrates good quantitative agreement with experiments for the zero-phonon line of the triplet-triplet transition. Finally, I will illustrate challenges associated with this method for determining the energies and orderings of the complex spin multiplets in FeAl. Learn more online at: http://www.ipam.ucla.edu/programs/workshops/workshop-ii-model-reduction-in-quantum-mechanics/?tab=schedule