 | Acta Crystallographica Section D Acta Crystallographica Section D BIOLOGICAL CRYSTALLOGRAPHY |
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![[Figure 1]](be5087fig1mag.jpg)
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Figure 1
An Argand diagram illustrating the structure factor of a reflection with significant anomalous scattering contribution. The brown vector represents the contribution of normally scattering atoms, FN; the red and purple vectors relate the normal, FA, FA′, and anomalous, ±FA′′, contributions of the anomalously scattering substructure for two Friedel mates; the two black vectors show the total structure factors for each of the Friedel mates, FT+ and FT−; the blue vector shows the total average structure factor FT. In the SAD experiment only the amplitudes (lengths) of FT+ and FT− are available (the ends of black vectors must lie on the circles of appropriate radii), but if the anomalous substructure is known, the size and orientation of the red/purple vectors can be calculated. The purple ±FA′′ vectors must end up on the corresponding circles. To calculate the electron-density map, the total structure factor should be used, with amplitude |FT| ≃ (|FT+| + |FT−|)/2 and phase φT. |
![[Figure 1]](be5087fig1.jpg)
| BIOLOGICAL CRYSTALLOGRAPHY |
ISSN: 1399-0047
