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Figure 2
Schematic illustration of PSAD for the case of model refinement against the SAD function. The three contour plots (a)–(c) are shown as a function of the assumed complex value of F−*; in each contour plot the cross indicates the origin and the black circle indicates the measured value of FO- for which the function values shown in (d) are taken. (a) The first (Sim) component of PSAD, P(F−*|H−*), is shown in blue contours centred on H−* (blue arrow). Compared with the SAD phasing case, the full scattering model is more complete, which increases the magnitude of H−* and decreases the variance in this distribution. (b) The second component of PSAD, P(FO+|F−*, H+, H−*), is shown in red contours centred on the expected vector difference between F+ and F−* (tail of red arrow). (c) The product of the two components of PSAD is shown in magenta contours. PSAD is given by the integral of this surface under the black circle. (d) The components of PSAD are shown as a function of the assumed value of α, with P( FO-, α |H+, H−*) shown in blue, P( FO+| FO-, α, H+, H−*) shown in red and their product in black. The three distributions have been normalized to place them on a common scale.

Journal logoSTRUCTURAL
BIOLOGY
ISSN: 2059-7983
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