Dynamical structure factors in binary liquids. I. Molten RbBr

Expressions for the spectral functions of number and charge density fluctuations are obtained for a binary fluid using Mori's memory function approach. Numerical calculations are done for liquid rubidium bromide and the results are compared with molecular dynamics and neutron inelastic scattering data. It is found that the theory reproduces very well the density fluctuation spectrum without any adjustable parameter. In the case of charge fluctuations, the theory predicts optic-mode peak at small wavenumbers. The peak positions are also in good agreement with molecular dynamics results. At large wavenumbers the agreement is again semiquantitative.