Single-particle motion in liquid and supercooled Mg70Zn30 alloy

We have calculated the velocity autocorrelation functions (VAF) in a self-consistent mode-coupling (MC) approach for liquid and supercooled Mg70Zn30 and have compared these results with data obtained in molecular-dynamics (MD) simulations. We have used a simple Gaussian ansatz for the 'binary' part of the memory functions while the MC contributions contain the coupling of the density fluctuations. The intermediate scattering functions, required in these MC integrals, are calculated in the viscoelastic approximation whereas the incoherent scattering functions are determined in a self-consistent manner from the VAF. In the direct comparison with MD-data agreement between the theoretical and the simulation data is observed for the liquid alloy while the discrepancies encountered in the supercooled state are found to be due to the viscoelastic approximation for the intermediate scattering functions. (C) 1999 Elsevier Science B.V. All rights reserved.