The crystal structure of all-silica zeolite Y (SiO2-FAU) was taken from experimental data. Aluminosilicate models containing different amounts of framework Al atoms and chargebalancing protons, labelled H-FAU_NH (with N = 1, 2, 3, 16, 32) were generated from this initial structure. On the one hand, highly siliceous models containing 1, 2, or 3 Al atoms and protons located within a single twelve-membered (12MR) of the FAU unit cell were considered, including two possible arrangements for H-FAU_2H (_1_3 = next-nearest and _1_4 = opposite, as shown in Figure ). On the other hand, more Al-rich models having one/two Al atoms and protons in every 12MR were prepared. It was always assumed that the framework protons are bonded to O1 oxygen atoms, as this constitutes the energetically most favourable proton site in the accessible pore space of FAU. Details of all models are compiled in Table . Each structure model was optimised using GULP, 67 relaxing all atomic coordinates and cell parameters, but fixing the cell dimensions to a cubic metric. These optimisations used the SLC (Sanders-Leslie-Catlow) potential parameters. In the subsequent DFT and AIMD calculations, the cell parameters were fixed at the FF-optimised values listed in Table .