Routine solution of 15-30 non-hydrogen atom structures was not demonstrated at the first SDPDRR (Structure determination by Powder Diffractometry Round Robin - see also the CPD Newsletter N°25), in June 1998. If more than 70 potential participants downloaded the data, only two solutions were provided for the pharmaceutical sample (~30 non-H atoms), and none for the inorganic one (15 non-H toms).

More than four years later, we observe that the number of structures solved by SDPD remains below 100 per annum, in spite of an explosion of the number of different software available for powder structure solution, commercial as well as in the public domain or even open source (TOPAS, DASH, PowderSolve, ENDEAVOUR, EXPO, MRIA, FOX, ESPOIR, PSSP, OCTOPUS, ROTSEARCH, FOCUS, SAFE, EAGER etc). 

It is time to verify if SDPD on demand has now really become routine, meaning that software in other hands than those of their developers can produce regularly the solutions. Many attendees of the XIXth IUCr Congress, Geneva (August 2002) were clearly impatient to see this round robin organized.

The first SDPDRR was made knowing the cell. Thus, the indexing bottleneck was avoided. It will not be avoided this time, however, the round robin will consist in 2 separated steps : indexing, and structure solution and refinement because experts in indexing could be different from experts in structure solution.

At the end of step 1 (indexing), the results will be disclosed so as to allow possibly more participants at step 2. Note however that participants will receive a participant number at step 1, and if they participate too to step 2, they will keep that same participant number.

Anonymity will be ensured unless the participants want to disclose their identity.

We have prepared 8 samples, all powder patterns are experimental, with the exception of the sample 2 pattern which was calculated from a single crystal structure. 

Samples 1 to 3 are to be used at steps 1 AND 2 (whole SDPD).

Samples 4 to 8 are to be used ONLY at the indexing step 1 (a representative number of samples showing various problems
were requested during Geneva), but if you think that you can solve their structures too, why not to give a try ?

Even if not mentioned, impurity presence as well as systematic zeropoint error or even some preferred orientation are possibilities to have in mind...

Each sample(n).zip file contains the dataset in various formats (.dat for Winplotr instrum=0, Bruker .raw, Bruker .uxd, GSAS .gsa, XY column .xy, Philips .rd and finlly CPI .cpi formats, plus a .txt file including the peak positions list obtained by using PowderX). 

Sample 2
- Probable formula :Sr₅V₃(F/O/OH/H₂O)₂₂
- Capillary synchrotron data, wavelength = 0.79764 Angstrom.
- Data : sample2.zip
- See the pattern

Sample 3
- Probable formula C₆₁Br₂
- Cartesian coordinates (.xyz file) for the C₆₀ molecule
- Capillary synchrotron data, wavelength = 0.79764 Angstrom.
- Data : sample3.zip
- See the pattern

Sample 4
- Probable formula C₂₀H₁₂O₆
- Capillary synchrotron data, wavelength = 0.79776 Angstrom.
- Data : sample4.zip
- See the pattern

Sample 5
- Probable formula C₁₆H₂₆O₆
- Capillary synchrotron data, wavelength = 0.79776 Angstrom.
- Data : sample5.zip
- See the pattern

Sample 6
- Probable formula C₂₁H₁₅Bi₂O₉
- Capillary synchrotron data, wavelength = 0.79764 Angstrom.
- Data : sample6.zip
- See the pattern

Sample 7
- Probable formula C₇H₅BiO₄
- Capillary synchrotron data, wavelength = 0.79764 Angstrom.
- Data : sample7.zip
- See the pattern

Sample 8
- Probable formula Rb₇Cr₆F₂₅
- Reflection laboratory X-ray data from a Bruker D8 Advance diffractometer, CuKalpha.
- Data : sample8.zip
- See the pattern

Peak position hunting is software- and user-dependent. The round robin participants are encouraged to use the peak hunting software of their choice, though a list of peak positions is furnished for each sample, obtained by using the PowderX software (.txt files), doing our best. 

We consider that indexing is giving the correct cell parameters, not only a list of possibilities ordered by decreasing value of figures of merit. We expect only one cell proposal from every participants, for each sample (or at least for samples 1-3 from people making SDPDs routinely), together with the list of indexed peaks, and figures of merit, the name of the software (for indexing and peak position hunting), a statement telling if the cell was ascertained by applying CHEKCELL or  a whole pattern fitting decomposition program (if yes, the software name and the method name - Pawley or Le Bail fit, etc), and finally a space group proposal (tell if estimated manually or with a software help, give the software name, if any), plus explanations judged necessary (use of databases like CSD, ICSD, ICDD, etc).However, giving a list of possible unchecked cells ordered by decreasing value of figures of merit will be accepted too. All this should be given inside one file (either a PDF or a 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.

Robin Shirley passed on CDT files (converted from the PowderX peak list) ready for using the CRYSFIRE suite (including 8 indexing software). Have also a look at the new indexing program McMaille.
 

Send the results to : L.M.D. Cranswick : [email protected]

STARTING DATE : Monday 9th September
DEADLINE : Sunday 13th October
RESULTS DISCLOSED : Monday 14th October

For samples 1-3 only

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 : [email protected]

And after all, if you can also determine the structures of samples 4-8 without the molecular formula of some of them, then, why not ? Routine is supposed to be fast and quasi-automatic.

STARTING DATE : Monday 9th September (as soon as you have indexed samples 1-3 powder patterns -a few minutes-, you may start solving their structures)
DEADLINE : Sunday 17th November
RESULTS DISCLOSED : Monday 18th November