Crystallography Journals Online : IUCR Backfile Archive 1948-2001
Chemistry and Pharmacology
Abstract Theoretical expressions for R2 and RN2, indicator functions used in automated structure analysis, are given for space groups P1 and P\bar 1 as a function of σ21 = ΣPj = 1 f2j/ΣNj = 1 f2f (P is the number of atoms in the tentative structural model) and of a threshold a on the intensity data. It appears that R2 is only slightly dependent, RN2, however, is strongly dependent on a. If low-intensity reflections are eliminated from the data set, R2, and not RN2, thus remains a useful control function in testing the reliability of atomic positions Theory and experiment are shown to be in good agreement.
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