Fig. shows the experimental total structure factors S(Q), which were deduced from the intensities in Fig. using PDFGetX3. In addition to the familiar and expected features at approximately 2 and 2.5 Å 1 , the S(Q) shows a weak but distinct feature (shoulder) at around ⇠1 Å 1 , in both materials. We believe that this feature is related to the peaks at 1 Å 1 predicted by MD simulations shown in Fig. . This figure shows simulated partial structure factors of Li, K, Cs, and F in FLiNaK and FLiNaK-CsF (5 mol%). Note that FLiNaK was simulated with the neural-network potential, resulting in a larger number of ions and the larger cell volume compared to the FLiNaK-CsF (5 mol%), which was simulated using an AIMD method. Therefore, FLiNaK simulations show clearer peak in the region below about 2 Å 1 (Li-Li plot at the upper left in Fig. ). Although the resolution of AIMD results is worse than NNMD, it is apparent that partial structure factors in each column are similar to each other. Noticeable di↵erences in Li vs K and Cs are also visible.