Electronic Resource
[S.l.]
:
International Union of Crystallography (IUCr)
Acta crystallographica
33 (1977), S. 368-372
ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
The phase sum |q| of a quintet, φH + φK + φL + φM + φ- H - K - L - M = q, is controlled by the E's of the main reflexions H, K, L, M and -H-K-L-M and those of the 10 cross-reflexions H + K, H + L, etc. It is empirically shown that |q| and the sum S of the 10 cross-E's follow a linear trend, so that |q| can be predicted from S. In this way not only positive (q ∼ 0) and negative (q ∼ π) quintets can be found, but also enantiomorph-sensitive quintets (q ∼ ± ½π). In the primary stages of a phase determination of a non-centrosymmetric structure these |q| values can be used to introduce and maintain the enantiomorph. For polar space groups an enantiomorph-specific refinement procedure can be developed by introducing |q| values in a modified tangent formula.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0567739477001004
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