Open AccessPROCEDURE FOR SOLVING THE PROBLEM OF PHASE DEGENERATION RESULTING FROM DIRECT METHODS
Author(s) -
Hai-fu Fan,
J. Qian
Publication year - 1981
Publication title -
wuli xuebao
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.199
H-Index - 47
ISSN - 1000-3290
DOI - 10.7498/aps.30.594
Subject(s) - spurious relationship , degeneration (medical) , ambiguity , phase (matter) , set (abstract data type) , crystal structure , computer science , space (punctuation) , crystal (programming language) , symmetry (geometry) , component (thermodynamics) , mathematics , physics , crystallography , geometry , quantum mechanics , chemistry , medicine , pathology , machine learning , programming language , operating system
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.