ISSN:
1600-5724
Source:
Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
Notes:
A numerical test is carried out on the theory proposed by one of the authors [Allegra (1979). Acta Cryst. A35, 213-220], which derives three-phase invariants from the Patterson function. The method is checked with two structures already solved (P{\bar 1} space group). For the strong Sayre triples the calculated cosine invariants are generally positive; the negative invariants arise from relatively minor features of the Patterson background, and so are more difficult to obtain. With a suitable choice both of the error standard deviation and of the degree of sharpening of the Patterson function, the average value of the calculated cosine invariants within small subsets of Sayre triples is reasonably close to + 1, while that of the negative invariants is either smaller and positive or slightly negative. The agreement between the test calculations and the results obtained after structural refinement is much improved if the calculated amplitudes and an extended limiting sphere are used instead of the experimental data.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1107/S0108767383000653
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