[RMCProfile-users] Bragg fitting

[Igor Levin]

Hi Lemuel,

Insufficient weight is one possibility. I suggest that you use the
automated weight optimization option, which is part of the most recent
distribution. The description is in the latest manual for RMCProfile. It
will require a keyword weight_optimization and a file called
optimization.dat to be present in your working folder.   Then, you can set
all the weights in your .dat file to 1.0 and let the procedure take over.
It's quite effective.  Please let me know if you find the information in
the manual insufficient - I will help with setting it up.

Another possibility is a bug in the program. Before fiddling with weights,
I would generate a configuration with atoms displaced according to Gaussian
distributions having widths corresponding to the ADP values you get from
Rietveld.  Data2config has this option or you can do it some other way.
 Then calculate your Bragg in RMCProfile setting run time to zero.  You
should have a good agreement, similar to what you get in Rietveld.  If not,
most likely, there is a bug.

Best,
Igor



On Tue, Jun 25, 2024 at 12:16 PM Von Dreele, Robert B. via rmcprofile-users
<rmcprofile-users at shadow.nd.rl.ac.uk> wrote:

> Dear Lemuel,
> This is usually because there’s not enough weight given to the Bragg data.
> It might be best to increase its weight and then repeat the RMCProfile run
> from the beginning as you may have fallen into a minimum that would be
> difficult to get out of with out sufficient Bragg contribution.
> Besy,
> Bob
>
> From: rmcprofile-users <rmcprofile-users-bounces at shadow.nd.rl.ac.uk> On
> Behalf Of Lemuel Crentsil via rmcprofile-users
> Sent: Monday, June 17, 2024 11:26 AM
> To: rmcprofile-users at rmcprofile.org
> Cc: Lemuel Crentsil <lemuel.crentsil at chch.ox.ac.uk>
> Subject: [RMCProfile-users] Bragg fitting
>
> Dear all, I am currently trying to use RMCProfile to do a refinement on
> x-ray data. I have used RMCProfile before and I'm familiar with the set up
> files etc. . With this refinement, I get a very poor Bragg fit that doesn't
> match the fit that
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> Dear all,
>
>
>
> I am currently trying to use RMCProfile to do a refinement on x-ray data.
> I have used RMCProfile before and I'm familiar with the set up files etc..
>
>
>
> With this refinement, I get a very poor Bragg fit that doesn't match the
> fit that I achieved with GSAS. I used get_gsas_bragg to extract the
> required files and used the .cif file exported from GSAS to create the
> supercell with rmc6f.
>
>
>
> Any thoughts?
>
>
>
> Lemuel
>
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