Texture in powder diffraction

[rugfri]

Hello
the powder diffraction implementation includes the March-Dollase model for preferred orientation in the symmetric reflection mode.
Are the parameters of the March-Dollase model automatically retrieved and optimized during the calculation or should they be passed by the user?

I have a sample with a strong preferred orientation, so I would like to be sure how it is best to proceed.
In case it is possible to pass the preferred orientation parameters, how would one do in the simpack_powdermodel.py example?

Thank you in advance
Regards

[dkriegner]

The texture parameters in particular the preferred orientation factor can be fit more or less like other phase specific parameters. in simpack_powdermodel.py you would do the following changes:

         strain_gauss=0,
         strain_lor=0,
+        preferred_orientation=(0, 0, 1),  # example texture direction
+        preferred_orientation_factor=0.6,  # start value
     )
 
     settings = {
@@ -131,6 +132,7 @@ def main():
         ("primary_beam_intensity", (None, None)),
         ("displacement_specimen_displacement", (-1e-4, 1e-4)),
         ("displacement_zero_error_deg", (-0.01, 0.01)),
+        ("phase_LaB6_preferred_orientation_factor", (0.05, 5.0)),
     ):
         p[pn].set(vary=True, min=limit[0], max=limit[1])

note that the orientation itself can not be fit. (in principle this could be added easily, but it seems more clever to try few low index directions or know this from the measurements). Note that for internal reasons there are some preferred_orientation keys in the emission settings. ignore those.

[rugfri]

thank you!
works.