The disparity between the masses of the two components in a binary liquid system can lead to the appearance of a peculiar phenomenon
named “fast sound,” which was identified for the first time in Li4Pb several decades ago and later observed in other Li based alloys. However,
the exact characteristics and nature of this phenomenon and the reasons behind its appearance have not totally been identified yet. In this
work, we analyze the longitudinal and transverse current correlation functions of UO2 , Li4Pb, and Li0.17Pb0.83 , as obtained from ab initio
molecular dynamics simulations. We find that fast sound appears to occur in the two former systems but not in the latter. Additionally, we
discuss some of the properties of the liquid mixtures that may be related to the appearance (or absence) of the phenomenon, such as the
composition, the polyhedral structure of the melt, and the type of bonding in the system.
