Collective dynamics on a crystal composed by disparate-mass particles: Li22Pb5

The lattice dynamics of crystalline Li22Pb5 is studied by means of computer simulations. The calculated spectrum shows several bands corresponding to modes in which only the light atoms execute motions. The spectrum of acoust ic modes is found to be well separated from the high-frequency bands and is in all cases confined to frequencies below 4 meV. The results are shown to provide a clue for the understanding of the origin of the strong anomalous dispersion features found in the melt by experiment [Phys. Rev. Lett. 80, 2141 (1998)] and molecular dynamics simulations [Phys. Rev. E 58, 4568 (199 8)]. [S1063-651X(99)10003-5].