Dispersion of collective excitations in a metallic glass

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Abstract
The wavenumber-dependent vibrational spectra for longitudinal and for transverse excitations in a two-component metallic glass are calculated. The calculation is based on pseudopotential-derived interatomic forces, a novel variant of the cluster-relaxation technique for the determination of the equilibrium static structure and density, and on the recursion method for the computation of the vibrational spectra. For both longitudinal and transverse vibrations the dispersion relations for two distinct modes-corresponding to the acoustic and optic modes in a crystal-could be determined. At very long wavelength these modes correspond to collective density and concentration fluctuations, at short wavelength they can be identified with the incoherent vibrations of the two atomic species. For longitudinal excitations the results can be compared with recent neutron inelastic scattering experiments and good agreement is found.