In all five zeolites, the fluoride position with the lowest energy is associated with a four-membered ring. This result agrees with most experimental crystal structures (with the exception of STF, discussed above) and with the previous force field study of Pulido et al., who also observed a preference for positions at 4MRs. In fact, it has been recognized that fluoride anions exert a structure-directing effect favoring structures having a high density of 4MRs, as they tend to stabilize these rings. Beyond this, however, there are no clearly identifiable trends in the energetic ordering of different sites. For example, the preference for 4MRs might give rise to the assumption that positions at a vertex where two 4MRs meet should be particularly preferred.