Beartex by examples

Beartex-WIMV

Refines the Orientation Distribution

WIMV is the most demanding program in the package and you have to get to know it. WIMV determines the orientation distribution from 1 to 100 complete or incomplete pole figures using the WIMV algorithm (Matthies and Vinel, 1982). It provides an automatic conditional ghost correction. Pole figures need to have full circles (and need to be expanded if they have only been measured over a 180 or 90 sector), the extent in polar angle can be chosen from a min to a max. WIMV is applicable to any crystal symmetry (divided into 11 rotation groups, equivalent to the rotation parts of the 11 Laue groups). The number and extent of pole figures need to cover the whole 3d orientation space. This can be evaluated with program MIMA. For high crystal symmetry a single incomplete pole figure may be sufficient for minimum coverage, but more are recommended. If diffraction peaks hkl are overlapped, they can be separated in the WIMV analysis by assigning intensity (weight) contributions. It is possible to eliminate a pole figure from a list in addition to limiting its extent for the analysis. The program gives statistical information with RP0, RP1 error values (Matthies et al., 1988), texture index (Bunge, 1969) and texture entropy (Matthies, 1990).

Symmetry codes for the 11 rotation groups are given below (Schoenflies or International notation). They are on data and cfg files, the user does not really have to know the numbers unless he wants to edit the cfg files.

System	cubic	tetrag.	ort.	mon.	tric.	hexag.	trigon.
Point group	O	T	D4	C4	D2	C2	C1	D6	C6	D3	C3
		432	23	422	4	222	2	1	622	6	32	3
Code igb	7	6	5	4	3	2	1	11	10	9	8

Control parameters for the iteration procedure are explained below. In general it is wise to use the defaults.
itz [20] maximum number of iteration steps
abpro [1.] (in%) Stop if RP for each pole figure point is lower
vitpro [.3] (in%) Stop if convergence velocity is lower
peps [.05] (in%) RP0 level
izick [1] zigzag regime for iteration exponent r.
irp [0] Optimization criterion for starting ODF based on RP0(0) or RP1(1)
r [2.] starting value of iteration exponent. Lower value for sharp textures (e.g. 0.1).
rfak [1.1] factor changing r-value in zigzag regime
ianfsu [1] optimization of the starting ODF approximation. This somewhat slows the procedure but follows the WIMV concept of ghost correction. It is necessary for very sharp textures and/or poor experimental pole figure compatibilities. In this case the WIMV iteration cycle does not work and the starting approximation is the only information about the ODF.
rfanf [2.] exponent for the starting ODF approximation

In the case of a high FON (texture background), the WIMV concept additionally considers a FON optimization for definite correction of remaining ghosts. This is not included in the present BEARTEX WIMV version.

Select an input file. Default file is C:\BEARTEX\DEMO.XPE.

If you use the new Berkeley pole figure format, your experimental data file already has information on crystal symmetry and lattice parameters. The sample symmetryin WIMV is always 1 (triclinic). However, if the input pole figure data possess a sample symmetry it is maintained in the ODF. Additional averaging of the ODF to higher sample symmetries can be done later (CSEC). If crystal symmetry is missing you have to enter it along with lattice parameters. Lattice parameters displayed in grey are fixed by crystal symmetry and can not be changed. Note that texture calculations only require relative lattice parameters.
In the case of monoclinic crystal symmetry, the z-axis unique convention is applied (a=b=90º(g), as defined in the International Tables of Crystallography Vol. 1. p7.
Choose iteration parameters. It is recommended to start with defaults as explained above.

Next determine if you want to use all the experimental pole figures and select the desired a-range (min. max.).

If an experimental pole figure is an overlap of two or three different hkl's click on the hkl, then on Overlaps.
A new window will open which allows you to select the contributing hkl's and relative weights. The sum of weights has to add to 1.0

Pressing Run will start the ODF calculation which you can follow. If data are very bad the procedure will stop. Then modify the iteration parameters to see if you get convergence. You need sufficient experimental data for a full ODF space coverage otherwise the program does not run. This can be evaluated by first passing your experimental data through MIMA.

Exemples:

Thin film of mercury iodide deposited on a KCl substrate.