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Structure Determination by Powder Diffractometry Round Robin - 3 Organized by : A. Le Bail and L.M.D Cranswick
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Conditions Data Download
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"It is a decade since Armel Le Bail and Lachlan Cranswick issued a challenge
to the powder diffraction community to solve two crystal structures from
powder diffraction data alone. Despite a generous timescale of around six
weeks, there were less than a handful of correct solutions. Would the situation
be different today? I think so - but I do have a number of caveats. (...)
With all the diversity of methodologies presented in this newsletter, are
we nearer to saying that structure determination from powder diffraction
data is routine. My personal view is that for the general user, it is not.
(...) Perhaps then, Armel and Lachlan, we will all be ready for another
SDPD Round Robin." - Bill David -
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| Introduction
After the first SDPDRR (Structure determination by Powder Diffractometry Round Robin), in 1998, and the second in 2002, (reports in CPD Newsletters 25 & 29) we are now close to 1500 structures determined from powder diffraction data, 200 per year ! It is time again to verify if SDPD on demand has now become routine,
meaning that software in other hands than those of their developers can
produce regularly the solutions. Many method improvements and new developments
have taken place since 2002, including charge flipping or prediction, the
latter even not needing the diffraction data (see for instance the CPD
Newsletter 35).
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| Conditions of the SDPDRR-3
The SDPDRR-3 is very similar to the first SDPDRR which was proposed for 2 indexed powder patterns. Anonymity will be ensured unless the participants want to disclose their identity. We expect all details (see and get the form) gathered into a PDF or MS Word document, preferably compressed by Winzip, attached to the email. Be careful to not include your name inside that file if you want to keep anonymity. Send the results to : A. Le Bail : lebail@univ-lemans.fr Duration : 3 months.
If enough answers from various approaches are received, we will consider writing the conclusions up in a similar way to the CCDC blind tests.
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| Data Download
We have prepared 2 samples, all powder patterns are experimental. Even if not mentioned, impurity presence as well as systematic zeropoint error or even some preferred orientation are possibilities to have in mind... The samples.zip file contains the dataset in various formats (.dat for Winplotr instrum=0 or 10, GSAS, Bruker .uxd and .raw, and finally CPI .cpi formats). Download samples : samples.zip Details below :
Sample 1
Sample 2
After 12 weeks, 167 data downloads and 7 solution submissions from 5 participants :
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ROUTINE SDPD ? 
Lost in the maze, which button to press ? And when ? Above is a very partial randomized list of software/methods. A. Le Bail : lebail@univ-lemans.fr L.M.D. Cranswick : lachlan.cranswick@nrc.gc.ca |
