Combining direct methods with isomorphous replacement or anomalous scattering data. I

A direct-methods procedure has been proposed for separating the phase doublet resulting from the use of either isomorphous replacement or anomalous scattering techniques. The phase doublet is expressed as φ_H = φ′_H ± |Δφ_H|. Formulae combining the structure-factor relationships with the phase-doublet information are given. Problems concerning the practical applications are also discussed. A test calculation with the error-free data for the protein insulin showed a satisfactory result.