Sound Velocities and Entropies of Non-Simple Liquid Metals Based on the Percus-Yevick Phonon Description

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Abstract
Recently, Yokoyama, Ohkoshi and Young1 (hereafter I) reported calculations of ‘phonon dispersion curves’ and sound velocities of liquid Na, K, Rb and Pb by invoking a perturbation theory based on a zeroth order system of independent density fluctuations having wave indices between 0 and k 0 = 31/3 kD . They suggested that sound velocities of liquid metals can be well predicted by the phonon perturbation approach, the details of the temperature dependence of the structure factor at constant volume being important for this. With the increased availability of structure-factor data within the phonon region in k space,2 it has now become possible to extend the calculations of I to a variety of non-simple liquid metals for evaluation of sound velocities. The aim of this short communication is to present such results which suggest the efficacy of the phonon method in this respect. The overall success of the calculations lend further credibility to the form of {∂ ln a(k/k 0)/∂ ln T}Ω proposed in I. This function is necessary input information into the calculations but, unfortunately, has not been measured with accuracy; a form applicable to all liquid metals near their melting points is suggested in Figure 1 of I.