Understanding the many-body electronic structure of the nitrogen-vacancy center in diamond*

Understanding the behavior of the ground and excited states of the negatively charged nitrogen vacancy center (NV^-) in diamond under pressure is of fundamental interest to probe superconductivity in diamond anvil cells. The nature of the ground (³A₂ triplet) state and of photoluminescence signals were first identified using optically detected magnetic resonance,  however the symmetry and position of the singlet energies with respect to the ground state are still under debate. In the present work, we combine first-principle generalized DFT calculations with an in-house extended Hubbard model to describe the defect many-body energy states. Using DFT-HSE06 and the ΔSCF method, we performedcalculations of the ground state and of some excited states total energies, which we used to parameterize our Hubbard model. Inclusion of interactions beyond the intrasite and intersite correlation terms turns out to be necessary to properly describe the correlated singlet-singlet transitions under pressure.