Frequency sum rules and charge fluctuation spectra in binary ionic mixtures

The explicit analytical expressions of the fourth and sixth frequency moments of the number density correlation functions of binary ionic mixtures in a uniform background are given for any concentration. Using the memory function formalism, we analyse the molecular dynamics results (MD) for charge fluctuation spectra of equimolar H+−He++ mixtures for different coupling parameters. The use of the frequency moments allows us to determine the memory function in a systematic manner. The agreement is good except for long wavelength.