The calculations reported in this work have delivered insights into structure, energetics, vibrational properties, and dynamic behaviour of AlPO 4 -H3. It has to be reiterated that this system is only of limited relevance to applications due to its small pores and the resulting low water uptake, however, the methods applied here could easily be transferred to other AlPOs that are currently considered as promising adsorbents for thermal energy storage (e.g. AlPO-34, AlPO-18, LTA-type AlPO). A key issue for these larger-pore systems is the construction of starting models of the hydrated structure. Even if the crystal structure of the hydrated form has been reported (as is the case for AlPO-34 and AlPO-18 ), the H-bond network will typically be less ordered than in AlPO 4 -H3, meaning that the setup of the starting structure would need to consider several possible arrangements. Another potential problem is a lack of long-range ordering of the Al-coordinated water molecules, which could be bonded to different framework Al atoms in different unit cells. In principle, it is possible to predict the most likely positions of the Al-coordinated water molecules by performing calculations for several partially hydrated models, as done previously for AlPO-11 . However, it has to be kept in mind that such partially hydrated phases are thermodynamically metastable, and that the interaction with "pore" water molecules will contribute to the stabilisation of an Al-coordinated water molecule in a given position. An analysis of the vibrational spectra in the O-H stretching frequency range can provide insights into the relative importance of shorter/stronger and longer/weaker hydrogen bonds in hydrated AlPOs; however, a direct assignment of an observed band to one particular water molecule in the structure will normally not be possible. Even in AlPO 4 -H3, where the water molecules are highly ordered, some bands stem from displacements of two H atoms belonging to different molecules, and such overlapping contributions will become more pronounced in more complex structures. In contrast, the "framework modes" attributed to Al-coordinated water molecules should remain largely unaffected, and they could become a useful indicator for the presence of Al-coordinated water molecules. Finally, the AIMD calculations show that dynamic effects are important even in this well-ordered structure. The inherent limitations of a purely static approach are especially well visible when trying to reconcile the calculated equilibrium position of H 2 O(pore) with the experimentally observed position. Given the ever-increasing computing power, AIMD calculations should become more and more routinely feasible in the future, and the field of porous materials provides a wide range of potential applications besides hydrated zeotypes, such as the dynamic behaviour of gases like CO 2 in adsorbent materials, the dynamics of extra-framework cations in charged-framework zeolites, and the behaviour of organic structure-directing agents confined to the pores of as-synthesised zeotypes .