High resolution Compton scattering study of Be

We have carried out high-resolution Compton scattering measurements from two single crystals of Be ([00.1] and [11.0]), together with highly accurate all-electron first-principles computations of the profiles within the band theory framework. The Compton data were collected using a newly constructed crystal spectrometer at a record momentum resolution varying between 0.023 and 0.032 a.u. (full width at half maximum) with 8 keV x rays from a synchrotron source. Although the overall shapes of the measured and computed spectra are in good accord, the fine structure in the data shows significant discrepancies with respect to the local density approximation based theoretical predictions. In particular, several features in the observed spectra are substantially broader than the computations, indicating the importance of electron correlations and other effects in analyzing momentum densities and Compton profiles from solids.