Both the XAS and NMR spectra were calculated on each configuration in the model independently and the outputs were summed across configurations to calculate the total spectrum. All spectral calculations, and electronic density of states were calculated at a plane-wave energy cut-off of 1000 eV and a single k-point at Γ in CASTEP v19.11 . The CASTEP gaugeinducing projector augmented wave (GIPAW) method was used to calculate all NMR parameters , at the PBE functional level of theory using the on-the-fly generated C18 library of pseudopotentials. The NMR parameters were averaged over 45 configurations from ab initio molecular dynamics (AIMD) with 48 Al atoms in each cell totalling 2160 Al NMR chemical shielding parameters for the a-Al2O3 model.