Negative tails in the velocity correlation function of supercooled liquids

The dynamics of supercooled liquid argon is investigated via a specific correlation function DeltaB. Its time behavior is well reproduced by taking into account the separate contributions of an Enskog-type diffusive part and of damped oscillations of vanishing time integral (nondiffusive part). The implications on the velocity correlation function (VCF) are investigated. Phononlike oscillations, also present in the crystal, can explain the first negative lobe and the subsequent shoulder of the VCF. The slow decay of DeltaB after the fast dynamics (t<1 ps) characterizes the liquid state, and produces negative VCF tails at long times (up to about 5 ps). (C) 2003 American Institute of Physics.