SDPDRR-3
Structure Determination by Powder Diffractometry Round Robin - 3

Organized by :

A. Le Bail and L.M.D Cranswick
February 2008


CLOSED
RESULTS AVAILABLE


 Introduction 
 Conditions
Data Download

 

IUCr Commission for Powder Diffraction Chairmanís Message, June 2007

"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 -
(see the full text in the CPD Newsletter 35)


  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).


  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.
STARTING DATE : Friday 1th February 2008.
DEADLINE : Wednesday 30 April 2008.

If enough answers from various approaches are received, we will consider writing the conclusions up in a similar way to the CCDC blind tests.


  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
- Probable formula : CaC4H4O6.4H2O
(yes a new calcium tartrate tetrahydrate polymorph)
- cell parameters : a = 8.222 A, b = 10.437 A, c = 6.249 A, alpha = 105.97, beta = 107.51, gamma = 94.94 degrees, symmetry : triclinic.
- CIF file corresponding to the previously known crystal structure (two determinations) providing the molecular formula
- Reflection laboratory X-ray data from a Panalytical diffractometer, CuKalpha
- Data : sample1.zip
- See the pattern

Sample 2
- Probable formula close to La14W8O45 or La8W5O27
- cell parameters : 
a = 9.039 A, c = from 32.60 to 33.65 A due to composition variation, symmetry : hexagonal
(formula and cell according to the ICDD-JCPDS cards 032-0502 and 032-0503, they may not be very accurate).
- Capillary synchrotron data, ESRF BM01, wavelength = 0.60044 A.
- Neutron data from the ILL, D2B, low resolution mode, wavelength = 1.5944 A.
- Data : sample2.zip
- See the synchrotron and the neutron patterns.


Cumulative histogram
After 12 weeks, 167 data downloads and
7 solution submissions from 5 participants :

 

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