Our AIMD simulations also reveal that the tin lone pairs dynamically reorient on a picosecond timescale (Fig. ). By comparing the results from our unrestricted AIMD simulations to equivalent data from simulations where the fluoride ions are fixed to their ideal fluorite positions, we have shown that orientational dynamics of the tin lone pairs is coupled to the dynamics of the nearby fluoride ions. This effect is modulated by the local cation arrangement: for tins with an asymmetric Sn/Ba nearest-neighbour configuration, the tin lone pair preferentially orients in the direction of other, nearby, tins. Hence, clusters of tin cations exhibit a cooperative effect where by the lone pairs on each tin tend to orient towards the interior of this cluster. This cooperative effect explains the dramatic disruption of the fluoride ion substructure in regions where several Sn cations are clustered together (Fig. ).