Ordering potential in liquid Li₄Pb and Li₇Ag₃calculated from neutron diffraction data

S CC (q) data obtained by neutron diffraction at different temperatures for liquid Li 4 Pb and Li 7 Ag 3 are used to calculate curves for W(r) which, according to Copestake et al. (1982, 1984) correspond approximately to the ordering potential V(r) at distances r larger than the hard-core diameter sigma . The authors find further support for this assumption from the fact that for liquid Li 4 Pb the ordering enthalpy Delta H ord introduced by Hafner et al. (1984), calculated from W(r) and the Fourier transform of S CC (q), is almost identical to the value given by Hafner et al., as it should be if W(r> sigma ) are really identical to V(r> sigma ). The diffraction data also yield meaningful values for the temperature derivative of Delta H ord . In all cases, the decreasing part of mod W(r> sigma ) mod behaves similarly to a Yukawa potential W y (r). If the effective interatomic interaction is assumed to arise from a positive charge at the Li site and a corresponding negative charge at the site of the other component, and if the electron screening is treated with the help of local pseudopotentials and the Thomas-Fermi approximation, the authors find that the amount of charge transfer in the two alloys is approximately the same and varies only a little with temperature. The electronic screening, however, is much stronger in Li 7 Ag 3 than in Li 4 Pb and increases significantly with temperature for the latter.