As measures of polarity, the calculated charges on S are +2.9 (IAO), +2.1 (Iter-Hirsh), and +1.6 (MAO) in the def2-QZVPPD basis set. The IAO charge may overestimate the polarity due to its minimal basis on S, while the MAO charge surely underestimates it, because the MAO orbital assigned to S is actually quite strongly polarized towards F. So while the MAOs themselves provide interesting chemical insight, they cannot resolve intrinsic limitations of population analysis. There are some limitations associated with reducing the union of the localized occupied orbitals and the AB2 antibonding orbitals to a set of MAOs that should be mentioned. First, some conjugated π systems, such as benzene and C 5 H 5 -, present a multiple minimum solution problem for orbital localization methods. Since our method relies on the localization procedure heavily, we expect there will be inconsistencies in these systems. For example, in benzene, there are different sets of solutions for the localized π orbitals, nominally corresponding to the two different Kekule structures. Using the Boys localized orbitals yields populations that reflect D 6H symmetry, while the Pipek-Mezey scheme gives alternating charges on successive carbons going around the ring. There is a second class of molecules that are inaccessible in our method. These are anions where the natural valence minimal basis is too small to provide an antibonding orbital for each bonding orbital. One such example is C 5 H 5 -, the cyclopentadienyl anion. Forming the set of AB2 valence orbitals and taking the union with the occupied space leads to a set of orbitals that cannot be localized to atoms. Broadly, we can say that neutral species with a single Lewis structure are wellhandled by the approach described here; as well as some more complex bonding situations like SF 6 discussed above.