For systems with significant static (strong) correlation, multiconfiguration methods are often used to describe the ground and excited states of molecular systems. The complete active space self-consistent field (CASSCF) method expresses the wave function as a linear combination of all possible configuration state functions that can be generated within a defined "active space" of n active electrons occupying N active orbitals. To get accurate electronic excitation energies and reaction energies, post-SCF methods such as the complete active space second-order perturbation theory (CASPT2) or n-electron valence state second-order perturbation theory (NEVPT2) can be used, as well as multiconfiguration pair-density functional theory (MC-PDFT). Multiconfiguration methods are desired as high-level (impurity) solvers in DMET because they can handle extended systems with multiple electronic configurations. Recently nelectron valence state second-order perturbation theory (NEVPT2) was implemented as a high-level quantum chemical solver within periodic DMET (pDMET) to capture dynamic correlation as a post-CAS-DMET procedure. However, even though NEVPT2-DMET is cheaper than NEVPT2, it scales poorly with the active space size and the parameter space (i.e. the number of orbitals in the impurity). A more affordable alternative for capturing electron correlation at the post-SCF level is multiconfiguration pair-density functional theory (MC-PDFT) and its hybrid version (HMC-PDFT). In a recent benchmark study of 373 vertical excitation energies from the QUESTDB dataset, HMC-PDFT was found to be as accurate or even more accurate than NEVPT2 for excitation energies. Here, we present a way to calculate the correlation energy starting from a CAS-DMET wave function using PDFT and hybrid PDFT. Our implementation is designed for systems with periodic boundary conditions (extended systems), specifically inspired by the class of problems we are tackling, such as point defects in crystals. It can be easily adapted to molecular systems with open boundary conditions. Here onwards, we refer to this approach as pDME-PDFT and we employ it to calculate singlet-singlet and singlet-triplet excitation energies in the F and M centers on the (100) surface of magnesium oxide. F centers play an important role in catalysis, energy storage, 37 photoelectrochemical applications and are responsible for several physical and chemical properties of MgO. M centers are an aggregate of two adjacent F centers, which also affect the physical and chemical properties of MgO, such as its electrical conductivity, magnetic behavior, and optical properties. 2 Theory