InternationalCrystallography of biological macromoleculesTables for Crystallography Volume F Edited by M. G. Rossmann and E. Arnold © International Union of Crystallography 2006 |
International Tables for Crystallography (2006). Vol. F, ch. 14.1, p. 296
## Section 14.1.8. The phase probability distribution for anomalous scattering |

From Fig. 14.1.8.1, it can be seen that the most probable phase angle will be the one for which . At any other phase angle, there will be an `anomalous-scattering lack of closure' which we define to be . The value of can readily be calculated as a function of ϕ (Matthews, 1966*b*; Hendrickson, 1979). Thus, if the r.m.s. error in is , and the distribution of error is assumed to be Gaussian, then from measurements of anomalous scattering, the probability of phase ϕ being the true phase of can be estimated using an equation exactly analogous to equation (14.1.4.2).

An example of an anomalous-scattering phase probability distribution is shown by the dotted curve in Fig. 14.1.8.2. The asymmetry of the distribution arises from the fact that is the phase probability distribution for rather than that of , which would be symmetrical about the phase of . The overall probability distribution obtained by combining the anomalous-scattering data with the previous isomorphous-replacement data (Fig. 14.1.2.1*b*) is given by and is illustrated in Fig. 14.1.8.2.

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*b*).

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