On the application of one-wavelength anomalous scattering. IV. The absolute configuration of the anomalous scatterers.
An essential first step in most techniques for using anomalous-scattering data for phase determination is to determine the positions of the anomalous scatterers. This is usually done by use of the anomalous differences, either as input to a direct-methods procedure or to produce a Patterson map. If the arrangement of anomalous scatterers is noncentrosymmetric then it is also necessary to find their absolute configuration and a process is described for doing this based on the properties of the P(s) function [Okaya, Saito & Pepinsky (1955). Phys. Rev. 98, 1857-1858]. If the arrangement of anomalous scatterers is centrosymmetric then the problem does not occur.