Spin-orbit coupling in solid-state spin defects from first principles

Optically active spin defects in solids, such as the nitrogen-vacancy (NV) and group-IV vacancy (G4V) centers in diamond, are promising platforms for quantum technologies and have been widely studied with first-principles methods to characterize their electronic, optical, and spin properties. Among these properties, spin-orbit coupling (SOC) plays a critical role, as it determines the zero-field splitting (ZFS) of high-spin qubit states and drives intersystem crossing (ISC) processes that enable optical initialization and readout of qubit states. In this talk, we present a computational framework for the calculations of SOC in spin defects that goes beyond density functional theory and avoids the use of cluster models to approximate spin defects in solids. The framework is general and broadly applicable to a variety of systems. We demonstrate its application to compute ISC rates of the NV center, highlighting the importance of going beyond mean-field descriptions. We further evaluate the SOC contribution to ZFS for G4V centers, comparing results of perturbative and state-interaction approaches. Our results underscore the importance of advanced first-principles treatments of SOC for accurate predictions of materials for defect-based quantum technologies.