The structure of the H2O molecule was first optimized using pcff and then re-optimized with DFT, using the same settings as for TCS. As discussed in more detail in the Results section, there is little point in comparing adsorption energies obtained for single water molecules to those of one TCS molecule per cell due to the vast difference in molecular size. For the case of protonated zeolites, experimental results and prior DFT studies indicate that an adsorption of clusters of several H2O molecules, which are large enough to deprotonate the framework, is energetically favored over the adsorption of single H2O molecules at the framework protons. Therefore, calculations aimed at a comparison of TCS and water adsorption considered clusters of eight H2O molecules. To study energetic trends among (H2O)N clusters of different size, additional calculations were done for models with N = 1, 4, and 12. Structure figures were prepared using VESTA.