Many-Body Green's Functions Theory in the GW approximation and Bethe-Salpeter Equation (BSE) has often been considered the method of choice for the calculation of electronically excited states (both charged and neutral) in hard condensed matter systems , starting from a mean-field ground-state reference often obtained from density-functional theory (DFT). Early studies in the late 1990s of inorganic crystals such as elementary semiconductors, or insulators such as magnesium oxide or lithium fluoride have been tractable because the atomic structure of these materials can be represented by small unit cells with only a few atoms . Nowadays, efficient implementations with periodic boundary conditions (PBCs) coupled with recent methodological developments and increased computing power have allowed treating larger systems, such as reconstructed surfaces, defect structures, or in general materials with more complex structures .