Example 1: simulation of a Laue diagram
As an example, we shall describe all the steps
necessary to draw the simulated Laue diagram
presented at the begining of this document.
It corresponds to a quartz crystal with the c axis
parallel to the X-ray beam. This is a full
example with the computation of intensites
because the structure is known. In other cases some
steps described here may be skeeped which make the
simulation simpler.
The asymetric unit is made of two atoms: oxygen and silicon.
Select first the "New a.u." button in the "File" pulldown menu.
Enter the first atom of the asymetric unit,
whose coordinates are X=0.4141, Y=0.2681, Z=0.785467 and
kind is O (Oxygen). Then click on "Add new atom". This
validates the informations entered in the menu, and allows you
to give the second atom with coordinates X=0.46987, Y=0.0,
Z=0.666667 and kind Si (Silicium).
Click the "OK" button to validate the
information entered, and close this menu.
The asymetric unit is now stored in memory.
Although it is not mandatory, it is a good idea to
save it immediately in a file.
During a later run one may read again this file,
thus it will not be necessary to enter again the same
information.
For this purpose, use the option "asy unit" of the "Save" button
in the "File" pulldown menu.
Select the "Crystal" button in the "Data" pulldown menu.
In the new menu,
select the crystal system "Trigonal".
Then press the "Select space group" button. Choose
"P 32 2 1" space-group.
Click the "Cell parameters" button to give the
parameters of the cell which are a=4.9134, b=5.4052, alpha=90
and gamma=120 degres.
Finally press the "Close" button to validate and close the
"Crystal data" menu.
Select the "Detector" button in the "Data" pulldown menu.
Give a
distance from crystal to detector equal to 4.1 cm, and a size of
16 cm by 16 cm.
We will simulate the diagram for the transmission case,
which is the default value, thus no other data are needed.
Select the "X-ray" button in the "Data" pulldown menu.
One chooses a conventional X-ray source.
Press the "Source characteristic" button,
and give the
voltage of the tube: for example 70 kV.
Select the option "1 axis" of the "Give" button
in the "Orientation" pulldown menu. Since the axis c of the crystal
points towards the X-ray source, give the coordinates 0 0 1.
This choice is available in the menu displayed when the
"Options" button of the "Simulation" pulldown menu is activated.
Choose 15 for the limits of the
indexes. Choose a wavelength range from
0.21 to 2.5 Angstroms. Finally, for the computation of
intensities, take into account all the proposed factors
by selecting all the buttons.
The computation of the simulation is made
by selecting the
"Compute" button of the "Simulation" pulldown menu. The cursor looks
like a watch during the
computation. Depending on the options, the structure, the power and
the load on your computer,
this time of computation may vary from a few seconds
up to several minutes.
At the end of the computation the cursor looks back its
usual shape and the result of the simulation is displayed in
the drawing area. Moving the cursor in this area
enables you to point to a Bragg spot.
Clicking this spot, the program will print, in
the window from where it was started,
all the information concerning
the spot: position in the detector axes,
Bragg angle, intensity,
list of the present harmonics, with their
wavelength, the inter-reticular distance
and the structure factor.
You may modify the display (and print) options
owing to the "Display" button in the "Simulation" menu.
For instance play with the
variable size of the spots, the response of the
detector, or the intensity threeshold.
When you have got a satisfactory simulation, you may
want to print it. This is possible
on any Postscript printer.
To create a Postscript file, select the "To file" option
of the "Print" button in the "Simulation" pulldown menu.
But you may also send the drawing directly to the printer
by using the "To printer" option of the "Print" button.
In this case, indicate the print command to use on your system.
If you want a detailed logfile
concerning the simulation,
select the "Write log" button in the "Simulation" pulldown menu.
Before exiting laueX, it is recommanded to save
your work: this avoids to give
the same parameters and options
during a later use of the program with
similar data.
Select the option "other data" of the "Save" button in
"File" menu. In the menu, give the name of the file
you want to create. Then click on "OK".