Exploration of the Optical Properties of Point Defects in Semiconductors and Insulators using Time-dependent Density Functional Theory

Optically active point defects in semiconductors and insulators hold great potential for quantum technology applications. First-principles investigations of excited state properties of point defects are instrumental in characterizing the defects through the interpretation of spectroscopic experimental results and the prediction of spin defects with tailored optical properties. Time-dependent density functional theory (TDDFT) enables the exploration of not only excited-state energies and wavefunctions of localized defect states but also potential energy surfaces by performing geometry optimizations. Here, I will present the study of the properties of several point defects using TDDFT, including the negatively charged nitrogen-vacancy center in diamond, the neutral silicon-vacancy center in diamond, the neutral divacancy center in silicon carbide, and the neutral oxygen-vacancy center in magnesium oxide. These calculations were made possible by our recent implementation of TDDFT with analytical forces in the West code. By using a GPU accelerated code and controlled numerical approximations, TDDFT calculations with hybrid functionals become feasible for systems comprising thousands of atoms, thus enabling detailed studies of excited-state geometries and finite-size effects of a wide range of point defects of interest to quantum technologies.