Preferred Orientation with Multiple Phases/Histograms

btrump1

I'm attempting to run simulated annealing using combined Neutron and X-ray data to solve a low temperature phase transition. After some work I've found two impurity phases and preferred orientation effects, which I am now accounting for. However, it doesn't seem to allow me to put the preferred orientation into multiple "for strs n to n" sections. Instead it gives the error:

"Parameter belongs to a parameter type that must have a unique name."

I've tried both PO(c, ang, hkl), PO(c, v, ang, hkl), and the raw code with PO_eng(c, ang), all of which give the same error. Likewise I've tried to set up the preferred orientation macros that Matthew Rowles put up, however this fails as well saying, "macro error & cosrho". What am I doing wrong?

Any help in this matter would be sincerely appreciated and I can provide my code it needed. Thanks!

rowlesmr

I can't remember the exact reason, but you'll need to put a separate PO correction in each str, you can't use the "for strs" construct.

I think that the unique prm name refers to the angle in the PO correction; if you put it in the for strs, you have a single prm name used in multiple strs, which constrains the values to be equal, where TOPAS needs the angle to be different for each str.

Matthew

alancoelho

Matthew is right; in Version 5 and earlier the PO correction be to be defined in each str. If you need to constrain the correction across the different strs then constrain the coefficients - to the same name for example.

Version 6 will allow for strs {} for the PO correction.
alan

btrump1

Excellent, moving this command to the str section has helped with that error, however now it seems to have a different problem. No matter where I put the command in the str section, the following line is not being read correctly. It either cannot read a string or ignores the following str command. I would guess this has something to do with the macro itself?

Sounds like I need to upgrade my version of Topas...

Thanks again!
-Ben

btrump1

After some playing it looks like it works fine if I don't include an angle. I'm guessing then that it has to do with the following part of the macro:

#m_ifarg ang ''"
#m_unique_not_refine ang
#m_endif

However, this is for a transmission experiment, hence I would think I should include a Pi/2 angle according to the document on the Wiki. I'm assuming then I would need to write a similar piece for when the angle is Pi/2?

Please forgive my ignorance, and I apologize for multiple posts. Thanks again!
-Ben

rowlesmr

Don't include an angle.

the angle in the PO macro is the angle between the preferred orientation vector and the current diffraction vector; just let Topas calculate it.

Your PO macro invocation should look like:

Preferred_Orientation(@, 0.8,, 0 0 1) 'note the two commas

By "transmission", do you mean capillary? If so, and you want to use my macros, you need to use:

PO_capillary_transmission(@, 0.8, 0 0 1)

btrump1

It turns out the problem I was having was simply with properly putting spaces into the macro:
PO(!r,0.8,,001) worked in some places in the file, while
PO(!r, 0.8,, 0 0 1) seems to work better, and has removed the error in some cases.

I do indeed mean capillary transmission, but if I'm reading your macro correctly, isn't the main difference the inclusion of a Pi/2 angle?

Thanks again, and again I apologize for my ignorance.

rowlesmr

Yes, you need to have spaces between the hkl values.

.

Pi/2 is the angle between the specimen vector and the diffraction vector (in the case of capillary)
The angle given by str_hkl_angle is the angle between the preferred orientation vector and the diffraction vector.

In Bragg-Brentano geometry, the specimen and diffraction vectors are parallel, so the difference in definition doesn't matter.

Have a read of: Ida, Takeshi. 2013. Effect of Preferred Orientation in Synchrotron X-Ray Powder Diffraction. Annual Report of the Advanced Ceramics Research Center: Nagoya Institute of Technology. http://www.crl.nitech.ac.jp/ar/2013/0711_acrc_ar2013_review.pdf.

My macro is equation 10.