Topas crash on combined Neutron and X-Ray refinement with magnetic structure

mathiasmorch

Hi everyone,

I'm currently trying to run some combined Neutron and X-ray refinements where I'm also describing a magnetic structure in the neutron data, but I've run into a problem where topas crashes. I'm running Topas v6

I'm using symmetry modes in the refinement, but have replicated that topas also crashes with a shubnikov approach.

The refinement is set up with 4 data sets: 3 data sets from 3 TOF detectors banks + 1 set of diffraction data from a synchrotron. All measured at room temperature from the same synthesis.

I can toggle back and forth where I enable the magnetic contribution to refine, but disable the X-ray data or disable the magnetic contribution to refine and enable the X-ray data and iteratively describe my data this way.

I've tried and failed to find a way to untoggle the magnetic contribution to the x-ray data: Is it possible to set a flag that disables the magnetic contribution or somehow enables a refinement with both the magnetic structure enabled and the x-ray data?

Best regards, Mathias

rowlesmr

I don't know how magnetic refinements work in topas, but are you able to define two structures by linking together all the relevant details, but one with magnetic bits and one without?

You'd then put the non magnetic one with the xray data, and the magnetic one with the neutron data.

Ie use two structures, not one.

alancoelho

Hi Mathias

Please send me a simplified version of your INP/data file and I will have a look.

Also, to work on only the x-ray part then remove the magnetic moment part; ie. something like the following will work:

  macro X_RAY_only { 1 }
   macro Mag_Stuff(text) 
      {
         #if (X_RAY_only)
         #else
            text
         #endif
      }
   str
      site ...
         Mag_Stuff(mlx...)

cheer
alan

johnsoevans

Dear Mathias,

You probably have this sorted by now. Just in case, I put an example of doing a magnetic neutron plus X-ray at the end of the magnetism tutorial:

http://community.dur.ac.uk/john.evans/topas_workshop/tutorial_lamno3_magnetic.htm

The INP file with "if Obj_There(neutron)" is at:

http://community.dur.ac.uk/john.evans/topas_workshop/data/lamno3_mag_x_n_combined.inp

John

mathiasmorch

Dear John, Alan and Matthew

Thank you for your help and suggestions!
I did not have the possibility to look at it again properly before today. Johns suggestions seemed the easiest to implement in my .inp and it worked perfectly, so thank you!

Best regards, Mathias

johnsoevans

Just for the record.....I didn't realise how easy the solution was until I talked to Alan :-) !

mathiasmorch

Yea, the solution is a lot simpler than i expected! :)

On that note i have a related follow up question that I haven't been able to find an answer to.
In the same tutorial that you linked you explain that the magnetic contribution to the pattern can be highlighted (and thus exported with "Save if Displayed..." if the user separates the nuclear and magnetic fits).
Is this this still the only possible way to extract the calculated magnetic contribution to a pattern or is there a keyword /code to distinguish this contribution in a magnetic refinements with shubnikov groups / symmetry modes?

johnsoevans

I think this is only possible with a "mag_only_for_mag_sites" str. You should be able to do mag_only_for_mag_sites with either Shubnikov or distortion mode approaches.