and to the use of a fixed covalent O-H bond length of 0.85 Å in the sc-XRD structure refinement, which is considerably smaller than the (more realistic) PBE-TS equilibrium value of 0.99 Å . Indeed, if the O• • •O distances are compared, experimental and PBE-TS distances agree within ∼0.05 Å for hydrogen bonds from H 2 O(2) and H 2 O(pore) to framework oxygen atoms (this includes the bifurcated H bond). However, agreement is less good for the two hydrogen bonds from H 2 O(1) to H 2 O(pore): Here, one O• • •O distance is 0.13 Å longer in the PBE-TS structure compared to experiment, whereas the other one is 0.21 Å shorter. A closer inspection reveals that the O11 oxygen atom of H 2 O(pore) moves approximately 0.2 Å along the channel during the DFT optimisation, causing the observed changes of the interatomic distances. As we will see below, when discussing the results of the AIMD simulations, H 2 O(pore) does indeed exhibit a rather large mobility in the channel, and it can thus be expected that the dynamic behaviour affects the average position of this molecule in the real structure at room temperature (the sc-XRD experiment was performed at T = 295 K).