RELEVANCE OF CHARGE-DENSITY MEASUREMENTS FOR HIGH-PRECISION CALCULATIONS

High-precision photon diffraction data in beryllium, diamond, silicon, copper and germanium are reanalysed with the aim of assessing the acc uracy of experimental X-ray and gamma-ray structure factors by compari ng derived values for cohesive energy with the thermochemical ones. Sp ecial attention is devoted to the diffraction data analysis for a mean ingful and accurate comparison between theory and experiment. A good o verall agreement of local density approximation calculations is found when the electron density exhibits spherical symmetry around each atom ic site. On the contrary, the analysis of experimental data in 3d tran sition metals, namely vanadium, chromium, iron, cobalt and nickel, poi nts out failures of the theory in reproducing the asphericity of the e lectron distribution.