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The met,hod of the one-electron density matrix determination from X-ray diffraction data is developed. It takes into account the translational symmetry and is applicable to covalent crystals. The crystal energies and directed Compton profiles are calculated in impulse approximation for silicon and diamond. The agreement with the experiments is rather good.Die Methode der Ein-Elektronen-Dichtematrixbestimmung aus Rontgenbeugungsdaten wird entwickclt. Sie beriicksichtigt die Translationssymmetrie und ist auf kovalente Kristalle anwcndbar. Die Kristallenergien und gerichteten Compton-Profile werden in Impulsnaherung fur Silizium und Diamant berechnet. Die Ubereinstimmung mit den Experimenten ist recht gut.

Self-consistent Sternheimer antishielding constants for chemical elements with nuclear charge in the range 2-94 are obtained within the framework of the local density approximation. The dependence of the Sternheimer factors on the ion charge states is discussed. These results can be employed for a prediction of the quadrupole splitting parameters on the basis of pseudopotential electron density calculations.