A better insight into this can be obtained by quantitatively comparing the ([BeF 4 ] 2 -) n cluster sizes between AIMD and NNMD simulations. To identify the ([BeF 4 ] 2 -) n clusters in the melt, the F-Be bond length was chosen to be 2.35 Å which was obtained from the r min value found in the F-Be partial PDF. The number of clusters of each size n were counted throughout the equilibrated NNMD and AIMD trajectories and were then normalized by the total number of Be atoms in each system. The distribution of cluster sizes larger than 2 is shown in Fig. A further insight of FLiBe structure as predicted in AIMD and NNMD simulations can be gained by bond angle distribution analysis as shown in Fig. . Both AIMD and NNMD predict average F-Be-F angle ∼108 • which corresponds to tetrahedral beryllium fluoride (Fig. ). The peak in Be-F-Be angle distribution (Fig. ) corresponds to corner-sharing beryllium fluoride complexes which lead to extended-range ordering in the melt. Both F-Be-F and Be-F-Be angle distribution plots are normalized such that their area integrates to one.