2) Computational Details 2.1) Structure models: FAU with an octahedral Al site A DFT-optimised structure of all-silica FAU constituted the starting point for the construction of models containing a framework-associated octahedral Al atom. The unit cell parameters were fixed to the cell parameters of all-silica FAU obtained in previous work (a = 24.227 Å). The model, in which the Aloct atom is located in the vicinity of a tetrahedral Al (Altet) atom, dubbed FAU_fwAloct_2Al in the following, was constructed along the lines of the work of Jin et al. The octahedral Al atom is coordinated to three framework oxygen atoms (Ofw) and three H2O molecules (unit cell composition: Si190Al2O382(OH)2(H2O)3, Figure ). The tetrahedral Al atom is in a next-nearest neighbour position of the Aloct site. Charge balance is ensured through two framework protons, one of them saturating the "dangling" oxygen atom that arises from the breakage of one Si-O-Al link around the Aloct atom, and the other one being bonded to an Ofw atom of a Si-O-Aloct link. Based on the FAU_fwAloct_2Al model, three models having fivecoordinated Al sites were constructed by removing one of the three water molecules. In addition, another model dubbed FAU_fwAloct_1Al was considered initially. In that model, there is no tetrahedral Al site and, consequently, only one framework proton.