For the FAU-and MOR-type all-silica zeolites as well as H-FAU and H-MOR, five configurations containing different arrangements of eight H2O molecules per cell were DFToptimized, and the Boltzmann-weighted adsorption energies were computed in an analogous fashion as for TCS. Figure shows the total adsorption energies and compares them to the TCS adsorption energies (full results for individual configurations are given in Table ). Even for the two all-silica zeolites, the total adsorption energies for the cluster are much more negative than for TCS, amounting to -389 and -427 kJ mol -1 , respectively. However, a calculation of the guest-guest contribution shows that larger part of the adsorption energy stems from H2O-H2O interactions, which are on the order of -295 kJ mol -1 for both zeolites.