Electron charge distribution of chromium

Abstract

A critical review of all the X-ray crystal structure factors of chromium has been performed. This showed that the low-angle X-ray atomie scattering (form) factors have been most accurately measured by electron diffraction and that, with correct choice of Debye temperature and analysis procedure, these are in excellent agreement with the best theoretical calculations. These aceurate form factors were found to be considerably less than those obtained from free atom calculations and the implications of these differences for bonding in chromium was investigated by generating a (110) deformation electron density distribution. This showed that bonding in chromium is achieved by the close-to-spherical depletion of electrons from atomie sites with redistribution such that there is a build-up of electrons in ⟨100⟩ and ⟨110⟩ between second and third nearest neighbour atoms with apparently very little charge density between nearest neighbour atoms in ⟨111⟩. These observations are consistent with the fact that the directional component of bonding in chromium is dominated by the 3d electrons which can arrange themselves so that the Cr atoms achieve closer packing in the b.c.c. structure than if they were spherical.