Local-environment fluctuations and vibrational spectra in substitutionally disordered alloys

We report calculations of the vibrational spectra for substitutionally disordered K₂₉{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.