Prior to discussing the results of the AIMD simulations, it is worthwhile to compare optimized unit cell parameters and F-Si distances to the experimental values. As reported in Table , the lattice parameters consistently agree with experimental values to within 1%, although a certain systematic tendency to overestimate the unit cell dimensions can be identified. The good performance of the PBE-D3 functional in reproducing experimental lattice parameters of assynthesized zeolites agrees with the results of a previous benchmarking study including various guest-free (calcined) zeolites and zeotypes. With regard to the F-Si distances, the experimental values obtained with XRD methods vary considerably, ranging from 1.84 Å for NON to 2.00 Å for CHA. It is well-known that the occurrence of fluoride disorder causes the apparent F-Si distances determined in XRD structure refinements to be longer than the actual distances, because the local environment that is probed by diffraction corresponds to an average over two different environments, SiO4 tetrahedra and [SiO4F] -trigonal bipyramids. It has to be noted that this argument does not explain the experimental F-Si distance of 1.90 Å in STF, where the fluoride anions are not disordered. As solid-state NMR methods probe the local environment, they can give more realistic F-Si bond lengths, provided that there is no dynamic disorder. For STF, NMR experiments delivered an F-Si distance of 1.72 to 1.79 Å, and values of 1.74/1.79 Å were obtained for SFF-type SSZ-44, where the XRD value amounts to 1.89 Å (the reported variation of NMR-derived distances for a given system arises from the application of more than one measuring method in the respective studies). The DFT optimizations deliver F-Si distances that agree very well with these values, ranging from 1.76 to 1.81 Å. Given the essentially identical bonding environment, the variation among different zeolites is non-negligible, with the shortest distance being found in NON, and the longest one in STT, a point that will be considered when discussing the dynamic behavior. It is worth noting that F-Si distances between 1.71 and 1.78 Å were reported in earlier DFT studies of all-silica zeolites containing [SiO4F] -units. 3.2 AIMD simulations: Dynamic disorder of fluoride anions