CHEKCELL: Graphical Powder Indexing helper and Spacegroup Assignment Software that links into the Crysfire Powder Indexing Suite by Robin Shirley
CHEKCELL now has a version of Truecell included with it under the "Cell Parameters" window. For tutorial runthroughs of Truecell in stand-alone mode, refer to the LMGP Suite Main Page
CHEKCELL can be obtained off the web at the the LMGP
(Laboratoire des Materiaux et du G�nie Physique de l'Ecole Sup�rieure de
Physique de Grenoble http://www.inpg.fr/LMGP/)
program suite site at
Sunday, 3rd December 2000: Bleeding Edge beta test versions of LMGP suite software such as Chekcell, Gretep and new programs are now available in the bleeding_edge_beta_versions/ subdirectory off the above download web addresses (wait 24 hours for the Canadian and Australian server to update). Please E-mail Lachlan Cranswick ([email protected]) with any bugs of Bleeding edge versions of the LMGP suite who will collate them and send them to the authors.
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The example data file is of poor quality data of a minor phase in halite. The unknown peaks were run through the
Crysfire Powder Indexing Suite by Robin Shirley. Crysfire can be run concurrently with Chekcell but this assumes you already have some trial cells from Crysfire in the Crysfire *.SUM summary file. In this demonstration, we will assign the cell manually, but use the CHEKCELL automatic spacegroup assignment option to get an indication of the best spacegroups for this sample. |
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Click on the CHEKCELL icon or run the program via the windows explorer/windows file manager to
bring up the CHEKCELL starting interface.
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You can then open a Powder diffraction data file using either the
File, Open, Profile menu option or the the bottom left
hand set of ICONs (Chekcell can presently use Siemens/Bruker RAW, CPI or RIET7 DAT
raw datafiles). In this case we open a liti.dat file. Chekcell will prompt for
the Wavelength of the peak file. Select Other and type in the wavelength: 1.54056
Angstrom (Cu k Alpha 1)
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pen a peak find/peak profile file either via the File, Open, Peaks File or
the ICON under the Measured Reflections tab.
The peaks will be displayed on the bottom window. (Celref can presently import Siemens/Bruker DIF,
Winfit *.DAT, or XFIT *.TXT peak find/peak profile output files). If loading an XFIT or related file
(in this case a liti.txt XFIT peak profile file),
when prompted for wavelength select OTHER and confirm the
wavelength being used (1.54056 Angstrom) and continue.
You will note that not all the peaks are assigned as the other peaks are due to halite. |
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Select the Cell Parameters tab and select the CRYSFIRE button bringing
up file open prompt to find the Crysfire *.SUM file.
Select the relevant Crysfire *.SUM file which will display the Cells summarised by Crysfire, and display the peaks expected from the first cell in the Crysfire file at the lowest symmetry spacegroup.
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Clicking on another cell will then calculate the expected lines for your graphical evaluation. From the below and above screen dumps, it might be obvious that the hexagonal 2.220, 3.501, 6.886, 90, 90, 90 is an OK cell to start with.
If you are still running Crysfire (and generating an updated *.SUM file), you can use the ReRead Icon to get an updated set of Trial Cells from Crysfire. |
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When you are happy with a cell and you wish to try and determine what might
be the most appropriate spacegroups, select the Best Group Icon
and if appropraite, edit the Tolerance. Normally the default is OK.
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Now select Start for ChekCell to
automatically sort the spacegroups in order of most likelyhood. In this
case it suggests P2221 is the most appropriate spacegroup for this cell.
Now it is up to you to determine which is the correct group (which may or may not be
one of the above). Either from Le Bail fitting or further deductions based
on your crystallographic experience.
You can now browse around trying this and other spacegroups. Or try another cell. The world is your oyster!
You can also graphically evaluate other spacegroups at Whim of course.
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Orthorhombic vs Cubic cells.The following relates to the above other cells found by the various indexing systems.Note from Jean Laugier of 11th April 2000From: "Jean Laugier" [[email protected]] To: "Lachlan Cranswick" [[email protected]] Subject: Error in Chekcell and Celref Date: Tue, 11 Apr 2000 17:53:32 +0200 I found a serious error in Chekcell and Celref. The Miller indices generator forgot lines when too close to another.This can be seen with the attached example (unix.sum and unix.txt). So the best determinated group can be different. This situation was verified for the orthorhombic solution (a=3.746 b=5.297 c=7.487) several lines are in fact groups of lines. This is a particular situation because in my opinion the best systeme is cubic (a*2*sqrt(2)~b*2~c*sqrt(2)~10.59) These relations are the best proof that this structure is cubic. |