This contrasts with the behaviour observed for SiO2-AST and GeO2-AST, where only oscillations around the cage centre occur. It is worth noting that the particular situation in AlPO4-AST also explains the evolution of the F-RMSDs with temperature: When most of the fluoride anions are bonded to a single Al atom during the whole AIMD simulation, their RMSD will be similar to that of the framework oxygen atoms due to the similar bond strength, as is indeed observed for 150 K.