While this is true for the F@Si12 site in STT, neither of the four positions in IFR that are associated with the basal 4MR, which shares two edges with other 4MRs, are lower in energy than the F@Si6_1 site. Furthermore, one might expect that "similar" building units also show a similar energetic ordering. This is, to a degree, true for the CHA is particularly interesting in this regard, as there is only one type of T site in the CHA framework. Since the local environment is identical for all four configurations considered, other explanations must be developed to rationalize the observed range of ΔErel values. In the first instance, one might envisage some relationship to certain interatomic distances between fluoride anions and OSDA atoms. For example, it would be reasonable to expect an inverse correlation between DFT energy and the distance from the fluoride anion to the positively polarized TMAda + nitrogen atom. However, an analysis of the three shortest F-N, F-C, and F-H distances in the optimized structures of CHA, compiled in Table , reveals no discernible correlation with the sequence of ΔErel values. As pointed out above, the two more favorable fluoride sites (F@Si1_2 and F@Si1_4) are associated with Si atoms at opposite ends of one equatorial Si-O-Si linkage (equatorial = the oxygen atom is part of the central plane of the d6r unit), and the less favorable sites are associated with the other equatorial linkage. A visualization of the respective structures in a projection along the c axis reveals that these equatorial linkages differ in their proximity to the screw axis, leading to shorter F-F distances of about 7.3 Å for F@Si1_1 and F@Si1_3 compared to ~8.4 Å for F@Si1_2 and F@Si1_4 (Figure ). While these distances are too long to expect any significant fluoride-fluoride repulsion, the number of Si-O-Si linkages between neighboring