Thermal diffuse x-ray scattering in simple metals

Calculations are reported for the ionic structure factor and x-ray scattering cross section of sodium (at T=0 and 90^∘K) and lithium (both isotopes at $T=0$^∘{}K) within the harmonic approximation. An evaluation of the appropriate displacement-displacement correlation function by the special-point method circumvents the need for a multiphonon expansion. In the case of sodium, the structure in the one-phonon scattering is straightforwardly accounted for and an approximate expansion is obtained for all multiphonon scattering. By treating core and conduction electrons on an equal footing it is shown that information on the conduction-electron system is present in the forward-scattering component. In lithium the one-phonon cross section at small angles aids in the determination of the effective electron-ion interaction.