Optical Properties of Neutral F Centers in Bulk MgO with Density Matrix Embedding

Theoptical spectra of neutral oxygen vacancies (F-0 centers)in the bulk MgO lattice are investigated using density matrix embeddingtheory. The impurity Hamiltonian is solved with the complete activespace self-consistent field and second-order n-electronvalence state perturbation theory (NEVPT2-DMET) multireference methods.To estimate defect-localized vertical excitation energies at the nonembeddingand thermodynamic limits, a double extrapolation scheme is employed.The extrapolated NEVPT2-DMET vertical excitation energy value of 5.24eV agrees well with the experimental absorption maxima at 5.03 eV,whereas the excitation energy value of 2.89 eV at the relaxed tripletdefect-localized state geometry overestimates the experimental emissionat 2.4 eV by only nearly 0.5 eV, indicating the involvement of thetriplet-singlet decay pathway.