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A method for analyzing powder patterns of phases of low symmetry
Author(s) -
Bartell L. S.,
Caillat J. C.
Publication year - 1987
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/s0021889887086205
Subject(s) - maxima and minima , triclinic crystal system , minification , symmetry (geometry) , computation , energy minimization , novelty , debye , algorithm , computer science , materials science , statistical physics , mathematics , physics , computational physics , biological system , geometry , crystallography , chemistry , mathematical analysis , mathematical optimization , computational chemistry , crystal structure , condensed matter physics , philosophy , theology , biology
A procedure for determining cell parameters from Debye–Scherrer intensities is described which has been successful in analyses of triclinic phases resisting previous methods of attack. It minimizes the difference between observed and calculated powder pattern profiles, the principal elements of novelty being several new strategies for avoiding entrapment in false local minima while steering the refinement in the proper direction. A preliminary model of the distribution of atoms in the cell is required to enable the computation of intensities. So far the method has been applied only to molecular crystals for which trial molecular coordinates could be generated with the aid of an energy minimization algorithm. Besides its discrimination against false minima, the procedure offers the advantages that provisional assignments of reflections never need to be made, and the overlapping of reflections, even in severe cases, causes no particular trouble.