PROCEDURE FOR SOLVING THE PROBLEM OF PHASE DEGENERATION RESULTING FROM DIRECT METHODS
直接法中相位退化问题的处理

A serious problem in the application of direct methods is the problem of phase degeneration. That is the phases of structure factors of a non-centrosymmetric crystal converge to a set of centrosymmetric phases. This would occur frequently in case of space groups P21, P41 etc. Phase degeneration gives rise to an additional centre of symmetry and hence a considerable number of spurious peaks in the resulting E-map leading often to the failure of direct methods. In this paper, a two step procedure of solving this ambiguity is proposed. In the first step, the crystal is treated as a centrosymmetric one and a mised image including both enantiomorphs is obtained, while in the second step, the actual structure is then derived from the mixed image by making use of the so-called "component relations". This method has been verified with a known structure and proved to be effective.