COLLECTIVE IONIC DYNAMICS IN A MOLTEN BINARY ALLOY

A recent experiment [Phys. Rev. Lett. 80, 2141 (1998)] showed heavily damped excitations in molten Li4Pb, within kinematic scales well beyon d those of hydrodynamic sound. These findings pointed to the presence of short-lived out-of-phase atomic motions as the underlying microscop ic phenomenon. A series of computer molecular dynamics studies are per formed to investigate the details of the atomic motions. From an analy sis of the simulated structure factors for molten Li4Pb, as well as by a comparison with those of liquid Li under different thermodynamic co nditions, it is found that the high-frequency excitation found in the alloy shows characteristics remarkably different from those of pure Li . The relative phases of the atoms partaking in such motions, as well as the remarkably short excitation lifetimes, portray it as a fairly l ocalized mode, with a frequency dependent polarization. [S1063-651X(98 )07210-9].