 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 3]](ba5036fig3mag.jpg)
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Figure 3
The effect of twinning by a twofold rotation about a on the diffraction pattern of a monoclinic crystal with β = 90°. Only the h0l zone is illustrated; the space group is P21/c. (a) h0l zones from a single-crystal. This could represent the diffraction pattern from one domain of a twinned crystal. (b) This is the same pattern as shown in (a), but rotated about a* (or h axis) (which is coincident with the a axis of the direct cell). This figure represents the diffraction pattern from the second domain of a twinned crystal. (c) Superposition of (a) and (b) simulating a twin with a domain scale factor of 0.5; that is, both domains are present in equal amounts. (d) Superposition of (a) and (b) simulating a twin with a domain scale factor of 0.2: the crystal consists on 80% of one domain (a) and 20% of the other (b). The values of |E2 − 1| for each figure are (a) and (b) 1.015, (c) 0.674, (d) 0.743. The ideal (untwinned) value of |E2 − 1| for this centric crystal structure is 0.97, meaning that its diffraction pattern characterized by the presence of both strong and weak reflections; intensities are more evenly distributed in acentric distributions, where |E2 − 1| has an ideal value of 0.74. |
![[Figure 3]](ba5036fig3.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
