We report calculations of the vibrational spectra for substitutionally disordered ${\mathrm{K}}_{29}$${\mathrm{Rb}}_{71}$ alloys. The calculations are based on pseudopotential-derived interatomic forces, a cluster-relaxation technique to determine the local fluctuations in the equilibrium interatomic spacing, and the recursion method for the calculation of the partial wave-number-dependent vibrational spectra, local and total vibrational densities of state, and Debye-Waller factors. The results—which are in good agreement with the results of neutron inelastic scattering experiments—allow one to study in detail the effect of mass disorder, force-constant disorder, and local-environment fluctuations on the vibrational spectrum.

• Received 28 June 1984

DOI:https://doi.org/10.1103/PhysRevB.30.7336