We utilized multireference methods, specifically CASSCF and NEVPT2, along with density matrix embedding, to determine the electronic transition energies between the singlet ground state ( 1 A 1g ) and singlet ( 1 T 1u ), triplet ( 3 T 1u ) defect localized excited states, within the bulk MgO's neutral oxygen vacancy. This is the first study in which a delocalized orbital corresponding to the CBM of g-symmetry was present in the active space. Our findings consistently support an optical transition involving the singlet defect localized states, and for this excitation, we observed linear trends as the DMET embedding space increases.