The experimental detection of octahedral Al atoms in zeolites has been established for decades, as they give rise to a characteristic signal at about 0 ppm in solid-state Al NMR spectroscopy (tetrahedral Al atoms: 50 to 60 ppm, reference: aqueous solution of Al(NO3)3). In contrast, the atomistic modelling of such sites is far from trivial, and different types of octahedral aluminium species have been proposed in prior computational work. Recently, Mancuso and Van Speybroeck employed a combination of DFT calculations and DFT-based AIMD simulations to investigate different types of framework-associated and extra-framework Al sites in H-ZSM-5, considering realistic conditions for methanol-to-hydrocarbon conversion reactions. They predicted two types of sites to be stable under operating conditions, one being a framework-associated [Al(OH)2] + species and the other one being a [Al(OH)2(H2O)2] + entity that exists as a "pore guest" that is not bonded to the framework. While both of these environments consisted of tetrahedrally coordinated Al atoms, they inferred that the presence of additional H2O molecules in the system could shift the equilibrium towards higher Al coordination numbers. The role of water was also investigated in a combined experimental and computational study of CHA-type zeolites by Jin et al. They identified two key factors that stabilise framework-associated octahedral Al sites, first, the proximity of framework protons (Brønsted acid sites) and, second, the presence of several additional water molecules in the vicinity ("wet" conditions). The zeolite model containing an octahedral Al atom used in the present work was constructed in analogy to the most stable model developed by Jin et al.', in which the framework-associated Aloct site is stabilised by two framework protons in the vicinity. This model was chosen because it seems reasonable to assume that octahedral Al atoms are dominantly present as framework-associated species in hydrated samples that have not undergone harsh treatment. Throughout this article, FAU models containing frameworkassociated Aloct sites are labelled with the designator FAU_fwAloct.