## 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.

### Creating the asymetric unit:

• 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.

### Entering the crystal data:

• 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.

### Entering the detector data:

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.

### Entering X-ray data:

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.

### Entering the orientation:

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.

### Choice of simulation options:

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.

### Simulation of the diagram:

• 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.

### Display options:

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.

### Printing the simulation:

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.

### Writing a log file:

If you want a detailed logfile concerning the simulation, select the "Write log" button in the "Simulation" pulldown menu.

### Saving the data:

• 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".