Electron density distribution in α-iron:: A γ-ray diffraction study

High-accuracy single-crystal structure factors, complete up to sin theta/lambda=1.9 angstrom(-1) have been measured from alpha-iron at 295 K using 316.5 keV gamma radiation. A detailed description of the electron density distribution is presented in terms of a multipolar atomic deformation model. The charge asphericity due to preferential occupancy of the t(2g) subshell is much smaller than that reported hitherto from x-ray measurements but is in quantitative agreement with ab initio calculations, laying to rest discussions about failures of theory in reproducing the aspherical charge. The 3d(7) electron distribution in the solid is contracted by 8.9% relative to the free atom. The atomic radial scattering factor deduced from gamma-ray diffraction is found to be in contradiction with earlier experimental and theoretical work. Achievement of a reliable Debye-Waller factor is of vital importance in this context. The directed metallic bonds are characterized by topological parameters at the bond critical points. Attention is paid to the 3d-4s occupation problem. A consistent interpretation of the 3d spin and charge form factors favors the occupation d(7) in the metal as against d(6) for the atom.