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Figure 2
Correlation r(xG) between model intensities from structure A3 and intensities from an ensemble to which symmetry operators from four space groups have been applied: P41 (a), P43 (b), P4 (c) and P42 (d). For (a)–(d), the illustrated sections represent one unit cell sliced perpendicular to the a axis, which is the noncrystallographic fourfold symmetry axis of this triclinic structure. In space group P4 (e), the ensemble structure correlates nearly exactly with the triclinic model (both depicted as black atoms), reflecting the origin-shift peak at xmax = 0 in (c). For space group P42 (f), in contrast, the application of the origin shift xmax = ½c gives a triclinic model (blue atoms) that is different from the ensemble structure (blue + red atoms together), yet the calculated intensities from the blue and red models are identical. This explains why the peaks in (c) and (d) are both approximately equal to 1.0. Symmetry-operator symbols are as defined in International Tables for Crystallography (Hahn, 1996BB14).

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ISSN: 2059-7983
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