The probability of fluoride-ions occupying a given site can be interpreted as a relative free energy for that site. Fig. ) shows distributions of per-site relative free energies, calculated for each individual tetrahedral and octahedral site as ∆F site = -kT ln(P occ ), where k is the Boltzmann constant, T is the simulation temperature, and P occ is the probability of each site being occupied, calculated from the AIMD simulation. These distributions can be thought of as effective "densities-of-states" of the different tetrahedral and octahedral site types. In Fig. (c), we also show a vertical line corresponding to the point where 2/3 of all available sites are statistically occupied, assuming that sites are preferentially occupied in order of increasing relative free energy.