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Ab initio structure determination from severely overlapping powder diffraction data
Author(s) -
Estermann M. A.,
McCusker L. B.,
Baerlocher C.
Publication year - 1992
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s0021889892004862
Subject(s) - diffraction , ab initio , intensity (physics) , fourier transform , function (biology) , powder diffraction , set (abstract data type) , point (geometry) , physics , algorithm , molecular physics , chemistry , crystallography , mathematics , optics , mathematical analysis , computer science , geometry , quantum mechanics , programming language , evolutionary biology , biology
A new method for unravelling the intensities of severely or exactly overlapping reflections in a powder diffraction pattern has been developed. The fast iterative Patterson squaring (FIPS) method involves an iterative procedure in which (1) a Patterson function is calculated using equipartitioned data (intensity ratio for overlapping reflections set to 1.0), (2) each point in the map is squared, (3) the new map is back‐transformed to obtain new Fourier coefficients, and (4) these coefficients are then extrapolated to give a new set of | F | 2 overlap hkl values and a new intensity distribution for the overlapping reflections (non‐overlapping ones remain unaffected). The cycle is repeated until the intensity statistics of the overlapping reflections approximate those of the non‐overlapping ones. Only after a redistribution of the intensities by the FIPS method was the ab initio structure solution possible for the molecular sieve SAPO‐40 (structure‐type code AFR), in which 65% of the reflections severely overlap.