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ExtSym: a program to aid space-group determination from powder diffraction data

DOI: 10.1107/S0021889808031087 DOI Help

Authors: A. J. Markvardsen (ISIS Facility) , K. Shankl (ISIS Facility) , W. I. F. David (ISIS Facility) , J. C. Johnston (ISIS Facility) , R. M. Ibberson (ISIS Facility) , M. Tucker (ISIS Facility) , T. Griffin (ISIS Facility) , H. Nowell (Diamond Light Source)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Applied Crystallography , VOL 41 , PAGES 1177-1181

State: Published (Approved)
Published: December 2008

Abstract: Once unit-cell dimensions have been determined from a powder diffraction data set and therefore the crystal system is known (e.g. orthorhombic), the method presented by Markvardsen, David, Johnson & Shankland [Acta Cryst. (2001), A57, 47-54] can be used to generate a table ranking the extinction symbols of the given crystal system according to probability. Markvardsen et al. tested a computer program (ExtSym) implementing the method against Pawley refinement outputs generated using the TF12LS program [David, Ibberson & Matthewman (1992). Report RAL-92-032. Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, UK]. Here, it is shown that ExtSym can be used successfully with many well known powder diffraction analysis packages, namely DASH [David, Shankland, van de Streek, Pidcock, Motherwell & Cole (2006). J. Appl. Cryst. 39, 910-915], FullProf [Rodriguez-Carvajal (1993). Physica B, 192, 55-69], GSAS [Larson & Von Dreele (1994). Report LAUR 86-748. Los Alamos National Laboratory, New Mexico, USA], PRODD [Wright (2004). Z. Kristallogr. 219, 1-11] and TOPAS [Coelho (2003). Bruker AXS GmbH, Karlsruhe, Germany]. In addition, a precise description of the optimal input for ExtSym is given to enable other software packages to interface with ExtSym and to allow the improvement/modification of existing interfacing scripts. ExtSym takes as input the powder data in the form of integrated intensities and error estimates for these intensities. The output returned by ExtSym is demonstrated to be strongly dependent on the accuracy of these error estimates and the reason for this is explained. ExtSym is tested against a wide range of data sets, confirming the algorithm to be very successful at ranking the published extinction symbol as the most likely.

Journal Keywords: Powder Diffraction; Extinction Symbol Determination; Space-Group Determination; Probabilistic Methods

Subject Areas: Information and Communication Technology

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Added On: 19/08/2009 23:07

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Computing & software technologies Information & Communication Technologies Data processing

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