  The attenuation rate of vibrational excitations in various metallic liquids
and glasses has been reported to change from the quadratic dependence on
wavevector at low wavevectors to the linear dependence at high wavevectors.
However, the origin of this behavior is not clear. Here, the analysis of this
phenomenon through molecular dynamics is presented for prototypical metallic
liquids, Cu56Zr44 and Fe. It is shown that the crossover wavevector is strongly
correlated with the structural coherence length characterizing coarse-grained
density correlations. We suggest that the linear dependence is caused by
scattering of vibrational excitations by structural activation processes with
low activation energies which are distinctively observed in metallic systems.
