[CCP14 Home: (Frames | No Frames)]
CCP14 Mirrors: [UK] | [CA] | [US] | [AU]

(This Webpage Page in No Frames Mode)

CCP14

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/)

Basic Demonstration of celref Unit Cell Refinement software on a CUBIC singlephase system

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

[Tutorials page] | [LMGP Suite Index]

CELREF: Graphical Unit Cell refinement.

7th September 1999 E-mail from Jean Laugier
"Generally I should like to make some remarks about the cell parameters measurements:
-The precision of the refinement of the cell parameters are not proportionnal to the number of peaks treated by the program. It is always better, when it is possible, to use peaks above 45°, mainly because the vertical divergence changes at this value. For a cubic structure, for example, it is better to measure only one peak at the maximum Theta angle than to use Celref with a lot of peaks, if the zero shift is weak or known!
-In the Least Square method it is assumed that the errors are random and in an experimental diagram the errors are totally systematic! It is necessary to be suspicious about the parameters precisions given by the program.
-The mathematical method does not work very well with cubic structures, if the starting a value is very different of the true value. it is always better to refine the zero shift in this case. (The batch bersion works in ILL since 20 years and nobody saw that! Probably they never refine cubic cells!).
Perhaps it would be necessary to make a special algorithm for the cubic case..."


WARNING: The following tutorial was done before Jean's above advice. The main purpose of this tutorial is to show how to interact with Celref. Thus the following tutorial may be non-optimal in terms of how you would handle a CUBIC material in reality.


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/

The example data file is of a cubic Y2O3 sample.


Click on the CELREF icon or run the program via the windows explorer/windows file manager to bring up the CELREF starting interface.


  • 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 (Celref can presently use Siemens/Bruker RAW, CPI or RIET7 DAT raw datafiles). In this case we open a Y2O3.dat file. CELREF will prompt for the Wavelength of the peak file. Select Other and type in the wavelength: 1.54056 Angstrom (Cu k Alpha 1)


  • Either type the reflections in by hand or open 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 y2o3.txt XFIT peak profile file), when prompted for wavelength select OTHER and confirm the wavelength being used (1.54056 Angstrom) and continue.


  • Select the Initial Cell Parameters tab.
    Input the (approximate) Cell, Spacegroup and calculation range information then press the Calc Button to generate the HKL listing. It is also possible to load this from a file if this information exists. Just click the File tab under the "Selected" Initial Cell Parameters tab which is done here (the y2o3.cry cell and spacegroup information file).


  • Select the Selection of the Reflections tab.
    To select the corresponding peaks, this can be done manually or automatically (with a controllable angular tolerance). Click on the Automatic Selection button to automatically select the corresponding peaks. Check both the top peak list and the bottom graphical representation to see that the selection has occured appropratiately. Peaks can be added or deleted manually. Be careful to check that Celref hasn't duplicated HKLs due to poor quality input data.


  • Select the Cell Refinement tab.
    At this point, recheck that the wavelength is correct, CELREF may be using the average alpha wavelength when you are profiled the peaks on the Alpha-1 wavelength. If you wish to change the wavelength, you can do this in the top left Current Values option area and click on the Red Change button.

    Click on the Compute button to perform the unitcell refinement. Two-theta offset can also be refined. If you click on this, Celref will prompt whether you wish to use model a constant zero shift or a sample exentricity. If you keep the unitcell constants at known values, the wavelength can be refined.


  • You can see all the results in a file using the Print ICON. Which is normally outputted in a file called celref.out

    ----------------------------------------------------
    No Title
    ----------------------------------------------------
     Number of reflections     :    52
     Max. number of refinement cycles   10
     Refinement constraints    : A=B=C
    
    Initial values    :
       Zero  Lambda     a       b       c     alpha   beta  gamma
     .00000  1.54056 10.6009 10.6000 10.6000  90.00  90.00  90.00
       1.    0.       1.      0.      0.       0.     0.     0.
    
    Recipr.lattice :   .0943   .0943   .0943  90.00  90.00  90.00
    Volume (a**3)  :  1191.113
    
     Number of refinement cycles       :     2
    
    
    Final values      : (Standard errors on 2nd line)
       Zero  Lambda     a       b       c     alpha   beta  gamma
     .00034  1.54056 10.6038 10.6038 10.6038  90.00  90.00  90.00
     .00003   .00000   .0000   .0000   .0000    .00    .00    .00
    
    Recipr.lattice :   .0943   .0943   .0943  90.00  90.00  90.00
    Volume (a**3)  :  1192.297
    
        H    K    L   2Th(obs)   2Th-Zero    2Th(Calc)     diff.
    
        1    1    2   20.519      20.519      20.518        .000
        2    2    2   29.170      29.170      29.168        .001
        4    0    0   33.804      33.804      33.803        .001
        1    1    4   35.921      35.921      35.920        .001
        4    0    2   37.935      37.935      37.934        .001
        3    2    3   39.862      39.862      39.861        .001
        2    2    4   41.713      41.713      41.713        .000
        4    1    3   43.501      43.501      43.500        .001
        5    2    1   46.910      46.910      46.910        .000
        4    4    0   48.546      48.546      48.545        .001
        3    3    4   50.141      50.141      50.140        .001
        4    4    2   51.695      51.695      51.698       -.004
        3    2    5   53.224      53.224      53.224        .000
        6    2    0   54.718      54.718      54.720       -.002
        1    4    5   56.189      56.189      56.188        .000
        2    2    6   57.632      57.632      57.632        .000
        1    3    6   59.052      59.052      59.053       -.001
        4    4    4   60.453      60.453      60.453       -.001
        3    4    5   61.833      61.833      61.835       -.002
        6    0    4   63.195      63.195      63.198       -.003
        3    6    3   64.541      64.541      64.545       -.005
        6    2    4   65.875      65.875      65.878       -.003
        6    1    5   69.798      69.798      69.796        .001
        0    8    0   71.079      71.079      71.080       -.001
        4    5    5   72.353      72.353      72.354       -.001
        4    4    6   73.618      73.618      73.619       -.001
        6    3    5   74.874      74.874      74.875       -.002
        6    0    6   76.123      76.123      76.125       -.002
        4    7    3   77.368      77.368      77.367        .000
        6    2    6   78.603      78.603      78.604       -.001
        2    7    5   79.838      79.838      79.835        .003
        0    8    4   81.061      81.061      81.062       -.001
        8    3    3   82.284      82.284      82.284        .000
        8    4    2   83.503      83.503      83.503        .000
        5    6    5   84.721      84.721      84.719        .002
        6    4    6   85.933      85.933      85.932        .001
        5    7    4   87.148      87.148      87.144        .004
        3    6    7   89.567      89.567      89.564        .003
        4    4    8   90.775      90.775      90.773        .002
        8    5    3   91.983      91.983      91.983        .000
        6    8    0   93.193      93.193      93.193       -.001
        7    2    7   94.405      94.405      94.405       -.001
        6    8    2   95.619      95.619      95.619       -.001
        3    9    4   96.837      96.837      96.836        .001
        6    6    6   98.057      98.057      98.055        .001
        5    6    7   99.282      99.282      99.279        .003
        5    5    8  101.740     101.740     101.739        .001
        4    6    8  102.980     102.980     102.977        .003
        1    9    6  104.220     104.220     104.221       -.001
       10    4    2  105.470     105.470     105.472       -.002
        7    8    3  106.730     106.730     106.731       -.001
        9    3    6  109.280     109.280     109.274        .006
    
    Sqrt(Sum(Th O-C)**2)/(Nref-Npar)) =    .000277
    
    Sqrt(Sum(2Th O-C)**2)/(Nref-Npar)) =    .000138


    [Tutorials page] | [LMGP Suite Index]

    [CCP14 Home: (Frames | No Frames)]
    CCP14 Mirrors: [UK] | [CA] | [US] | [AU]

    (This Webpage Page in No Frames Mode)

    If you have any queries or comments, please feel free to contact the CCP14