They possess distinct electronic states, including a singlet ground state and a triplet excited state. The optical properties of the F centers are highly tunable, making them suitable for a wide range of color-center laser applications. In particular, magnesium oxide (MgO), an ionic oxide, exhibits F centers that significantly influence the material's chemical properties, thus making it a promising candidate for optoelectronic and catalytic applications. The interesting properties of F centers in alkaline earth oxides can be attributed to their distinct electronic structure which results from the emergence of new local energy levels within their optical gap. F centers can trap one or two electrons within the anion vacancy, resulting in the formation of F + and F 0 centers respectively. The electrostatic stabilization effectively retains these electrons within the vacancy due to the large Madelung constant of the ionic crystal. In this study, we focus specifically on the neutral oxygen vacancy, the F 0 center in the bulk of MgO crystal, and aim to understand the optical transitions involved. The F 0 center in MgO has been extensively investigated. The optical absorption energy has been computed using quantum chemical embedded cluster approaches, periodic boundary conditions using equation of motion coupled cluster theory, quantum Monte Carlo 8 and many-body perturbation theory methods. Despite their seemingly simple nature, MgO F 0 centers are electronically complex, and there is disagreement between the molecular quantum chemical and solid-state calculations on the nature of the electronic states involved in the optical absorption and emission spectra. The absorption maxima has been experimentally determined to occur at 5.03 eV. The absorption process involving the midgap state can occur in two ways: (i) an electron is promoted to the conduction band minimum (CBM), known in literature as photoionization, or (ii) defect localized excitation to one of the higher energy triply degenerate states. Quasiparticle excitation methods and quantum Monte Carlo studies have suggested that the absorption maxima is due to the photoionization process, with the exception of the recent embedded-BSE study. On the other hand, wave-function based methods have always attributed the absorption maxima to the defect localized excitation. A report by Rosenblatt et al. measures a difference of 0.06 eV between the relaxed F 0 center excited state and the conduction band edge, suggesting that the two processes are energetically similar. Overall, there is an uncertainty of the states involved in the absorption process. The experimental emission bands have been detected at around 2.4 eV and 3.1 eV. The later has been ascribed to the F 0 center, interpreted to arise from a singletsinglet, triplet-singlet transition, recombination of midgap electrons with the valence holes or hole capture at an F + center. However, there is no definitive evidence that establishes which transitions correspond to the photoluminescence bands. The lack of a fundamental understanding engenders the need to seek a method which can affordably deliver an accurate quantum chemical description of the electronic interplay in MgO F 0 center. Furthermore, F 0 centers have degeneracy in the low-lying defect localized excited states, giving rise to strong electronic correlation. Computing electronic excitation energies in extended systems is still a challenge for ab initio quantum chemistry methods. Although density functional theory is commonly employed for periodic calculations, its single determinant nature is inadequate for addressing multireference systems. This is the reason one needs multireference quantum chemistry methods or the inclusion of many body effects through the Green's function method, to explore multiconfigurational systems, despite their steep computational scaling. Fortunately, strong correlation in point defect materials tends to be localized, implying that uniform accuracy throughout the quantum chemical model may not be necessary.