Dispersion of collective excitations of amorphous and liquid Zr₆₇Ni₃₃alloys

Abstract

Molecular dynamics simulations have been performed to study the collective excitation of Zr67Ni33 amorphous and liquid alloys with a pair functional potential. The spectrum and the correlation function of the particle current are calculated for longitudinal and transverse modes. The dispersion relation is estimated from the spectrum. It is related to the peak position of the static structure factor and is strongly dependent on temperature at large wavenumbers. The collective excitation is evident for the Zr-Zr correlation but not for the Ni-Ni correlation. The motion of the Zr-Zr correlation is non-localized but that of the Ni-Ni correlation is localized. The sound velocity and the Debye temperature are calculated from the dispersion relation. The calculated power spectrum agrees with the previously reported experimental result. The power spectrum of the Zr atom of the amorphous state is similar to that of the crystal state. On the other hand, the power spectrum of Ni shows an obvious difference between the amorphous and crystal states.