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Highly accurate single-crystal structure factors, complete up to sin /ϭ1.6 Å Ϫ1 , have been measured from CoO at 305 K and in the antiferromagnetic state at 10 K using 316.5 keV ␥ radiation. Moderate uniaxial pressure was applied in the low-temperature phase to force a single-T-domain sample. A detailed description of the electron-density distribution is presented. The occupancies of the 3d shell are computed from multipole refinement parameters, showing significant differences between the two magnetic phases. The spin and orbital contributions to the total magnetic moment of Co are derived from the experimentally determined number of unpaired electrons. Results are compared with ab initio calculations as well as with magnetic form factor measurements. A careful analysis of electronic properties in the internuclear regions reveals the Co-O interaction to be purely ionic. Its physical significance on the antiferromagnetism is discussed.

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Two errors in the paper by Wilson [Acta Cryst. (1993) AbstractThe maximum-entropy method (MEM) was applied to accurate y-ray diffraction data from MnF2 and NiF2 to explore details of the charge-density distribution. For a fair judgement of the results, Si Pendellrsung data [Saka & Kato (1986). Acta Cryst. A42, 469-478] were also treated. It is shown that conclusions drawn from MEM maps must be accepted with some reserve, particularly in the regions of interest in charge-density studies.

Several general properties of maximum-entropy maps are reviewed that substantiate previous results from selected applications. In particular, the maximum-entropy method (MEM) is depicted as a smoothing scheme and the intrinsic bias introduced by this procedure is pointed out. It is argued that the MEM is not well suited for accurate charge-density mapping.