Fig. ) shows the probability distribution (number frequency) of tetrahedral and octahedral sites in our AIMD simulation, subclassified by the number of Ba and Sn cations that coordinate each site. These figures also show the proportion of time during the simulation, or probability, that each type of site is occupied by a fluoride ion. For the tetrahedral sites, the occupation probability depends strongly on the identity of the coordinating cations: as the number of coordinating Sn increases the probability of that site type being occupied by fluorine decreases. Comparing the limiting cases of exclusive Ba-coordination and exclusive Sn-coordination, Ba 4coordinated sites are occupied nearly 100 % of the time, while Sn 4 -coordinated sites are nearly always vacant (raw numerical data are available in the Supporting Information). In contrast, for octahedral sites, the occupation probabilty depends much less strongly on the identity of the coordinating cations; each type of octahedral site is occupied approximately 2/3 of the time, although we do observe a weak preferential occupation of octahedral sites with equal numbers of coordinating Ba and Sn.