The DFT optimised tetragonal LLZO structure with its three Li Wyckoff sites: 8a, 16f, and 32g are displayed in The calculated lattice parameters, displayed in SI Table are in excellent agreement with reported experimental XRD data (within ∼ 0.6%). The calculated band gap of 5.92 eV is also in good agreement with experiments showing an optical band gap of ∼ 6 eV. Other DFT simulations using HSE06 show a similar band gap to our results and hybrid functionals such as HSE06 are known to accurately reproduce the electronic structure of semiconductors and insulators. The PBEsol bandgap is calculated to be ∼ 4 eV in line with PBEsol's typical underestimation of the bandgap due to the well known self-interaction error. 77,78