APPLICATION OF THE SPARSE DENSITY PRINCIPLE - A STATISTICAL EVALUATION OF THE PHASE AMBIGUITY IN THE SINGLE-WAVELENGTH ANOMALOUS SCATTERINGMETHOD (SAS)
P. Verwer et al., APPLICATION OF THE SPARSE DENSITY PRINCIPLE - A STATISTICAL EVALUATION OF THE PHASE AMBIGUITY IN THE SINGLE-WAVELENGTH ANOMALOUS SCATTERINGMETHOD (SAS), Zeitschrift fur Kristallographie, 206, 1993, pp. 45-55
The method of single-wavelength anomalous scattering (SAS) allows the
determination of structure-factor phases apart from a two-fold phase a
mbiguity. A statistical procedure is described, based on the joint pro
bability distribution of three structure-factors, in which a priori th
e influence of partial structural information is introduced (Giacovazz
o, C., Acta Crystallogr. A39 (1983) 685-692), which permits to calcula
te the relative probabilities of the two SAS solutions for each phase.
The relation of this procedure with the sparse density principle (i.e
. the assumption that rho(r)rho(-r) almost-equal-to 0) is indicated. A
possible application is the use of extra structural information, e.g.
information on atomic positions in a protein backbone, in the course
of a protein crystal structure determination.