Near-edge x-ray-absorption fine structure of Pb: A comparison of theory and experiment

Two independent techniques are used to obtain the background function for the x-ray-absorption fine structure (XAFS) of pure Pb at energies that are normally inaccessible because they are in the edge. The results of the two techniques are shown to give the same \ensuremath{\chi}(k) above a threshold energy in the absorption edge, where the background is 70% of the edge step. The reliability of the XAFS starting at unprecedentedly low k values (1.5 A${\mathrm{\r{}}}^{\mathrm{\ensuremath{-}}1}$ above the Fermi energy) allows sensitive tests of several details of theoretical XAFS calculations. Electron-hole-excitation losses in addition to the plasmon-pole loss term are shown to be important, and the Hedin-Lundqvist many-body self-energy is found to be superior to that of Dirac-Hara for pure Pb. One of the presented methods of background removal can be employed for general XAFS analysis, and is easily automated.