Static structure factor and electron-electron correlations in Be. A comparison of experiment with electron-gas theory

The inelastic scattering cross section of metallic Be has been determined from an x-ray scattering experiment. The conditions under which the electronic contribution (static structure factor) can be extracted from such an experiment are discussed together with the approximations which have to be introduced in order to distinguish between core and band contributions. Accordingly, the static structure factor and the exchange and correlation energy of conduction electrons in Be have been determined. These quantities agree within experimental accuracy (∼5%) with current electron-gas theory. From the static structure factor the electron-electron pair-correlation function has been deduced and compared with corresponding calculations for jellium. To this purpose the unavoidable experimental limitations on data accuracy and the theoretical difficulties which are encountered when performing direct first-principles calculations are discussed.