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Tutorials and Examples

LMGP suite for Windows by Jean Laugier and Bernard Bochu

(Laboratoire des Materiaux et du Génie Physique de l'Ecole Supérieure de Physique de Grenoble http://www.inpg.fr/LMGP/)

Using Celref to help Assign a Spacegroup after Powder Indexing

The CCP14 Homepage is at http://www.ccp14.ac.uk

[Tutorials page] | [LMGP Suite Index]

This tutorial now Obsolete

It is better to use the LMGP Chekcell program referred to in the main LMGP index page.

CELREF: Graphical Unit Cell refinement software can also be used as an easy visual guide to help assign a spacegroup to powder data after a possible cell has been found by Powder Indexing. This can be useful when dealing with moderate peak overlap and you do not have easy access to the IUCr International Tables. After finding out the most likely spacegroups, Le Bail extraction on these spacegroups might then be in order to see which gives the most appropriate fit.

If you wish to work from, you can use Equiv and Indx where you can quickly browse through the space groups and obtain their extinction conditions as a substitute for the IUCr International Tables.

(Note: Celref will read Philips, Bruker, CPI and Riet7/XFIT raw data files and Bruker, Philips, XFIT, Winfit and column peak find/peak profile files. The following example used XFIT to profile the peak positions but this is optional).

The following example uses a Lithium Titanate Phase ("New Phases Formed in the Li-Ti-O System under Reducing Conditions", I.E. Grey, L. M. D. Cranswick, C. Li, L. A. Bursill, and J. L. Peng, Journal of Solid State Chemistry, 138, 74-86 (1998)). A downloadable ZIP contains the raw data, an XFIT project file, XFIT result file and a celref CRY file (to save time inputting the cell values)

Cell and Unit Cell Dimensions as found by powder indexing using the Crysfire system:


CELREF can be obtained off the web at the the LMGP (Laboratoire des Materiaux et du Génie Physique de l'Ecole Supérieure de Physique de Grenoble http://www.inpg.fr/LMGP/) program suite site at http://www.ccp14.ac.uk/ccp/web-mirrors/lmgp-laugier-bochu/


Click on the CELREF icon or run the program via the windows explorer/windows file manager to bring up the CELREF starting interface. Open the data file (in this case liti.dat) with a Wavelength of "other" and input the wavelength of 1.54056. (If you get an error on opening, it could be some of the header information in the DAT file. So just remove the header and try again. Also, if Celref unzooms the 2-theta scale everytime you select a different spacegroup; download the latest celref which does not have this nuance.


  • It is option to import the XFIT peak file but this can make it easier to match up calculated lines with peaks. So now use the Measured Reflections, Get Bragg Reflections from a File option and load the XFIT peak result file.


  • Select the Initial Cell Parameters tab and from the keyboard add the cell and Cell parameters.
    • Monoclinic
    • a=14.0956 b=2.9524 c=4.8917 beta=92.1716

    (Be wary that if you are using cut and paste, right end spaces in the cell values will cause Celref to state that there is an error on that cell value.)

    As a default, give it the first monoclinic spacegroup on the list (P2). On the 15th March 2000 version or later of celref, this will automatically calculated the lines. Thus there is no need to press the Calc button.


  • Now all you have to do is click on the next spacegroup: or easier still, use the keyboard's down arrow key to quick scroll through the possible spacegroups.

    Be wary that some lines/HKLs can have near zero/zero intensity due to the atomic structure. A good indicator that you do have the correct spacegroup and cell, is the ability to determine a good atomic structure solution and refinement that will fit inside the cell using this spacegroup!

    • Spacegroup of P2 ==> P2

    • Spacegroup of P21 ==> P21

    • Spacegroup of C2 ==> C2

    • Spacegroup of PM ==> PM

    • Spacegroup of PC ==> PC

    • Spacegroup of CM ==> CM

    • Spacegroup of CC ==> CC

    • Spacegroup of P2/M ==> P2/M

    • Spacegroup of P21/M ==> P21/M

    • Spacegroup of C2/M ==> C2/M

    • Spacegroup of P2/C ==> P2/C

    • Spacegroup of P21/C ==> P21/C

    • Spacegroup of C2/C ==> C2/C


    Again, after finding out the most "likely" spacegroups, Le Bail extraction on these "likely" spacegroups might then be in order to see which gives the most appropriate fit.

    Again, a good indicator that you do have the correct spacegroup and cell, is the ability to determine a good atomic structure solution and refinement that will fit inside the cell using this spacegroup!

    Now you might try and solve the structure using a program such as the EXPO software from the Sirware group.


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