how to refine multiple phases

[Hao Lin]

Dear all,

I am a new users of PDFgui and now can do single phase refinement, but I have not found any examples using multi-phases. Could some guys  please give some instructions about how to refine multiple phases from scratch, how to correlate them and get their respective fraction? 

Thanks so much 

Hao Lin

[Simon Billinge]

Dear Hao Lin,

In short, when you create a fit in the fit tree, you select a single dataset, but you select multiple cif-files to use as models, one for each of your phases.  You set scale factor as a refineable parameter in each of the phases.

Look out for the upcoming book that should be published by OUP around October with examples of how to do all these things. 

S

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Simon Billinge

Professor, Columbia University

[Hao Lin]

Hi Prof. Billinge

Thanks so much for your answer and I appreciate it. I thought it required an equation to correlate two phases, like GSAS2 does. 

Hao 

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[Simon Billinge]

Dear Hao,

You can "correlate" variables between the phases if you want.   each phase has a bunch of "parameters" (like lattice parameter, ADP of the Na ion, etc.).  We assign these to "variables" using the "@56" method, so if we wrote @56 in the a-lattice parameter box of the gui, that would assign the a-lattice parameter of that phase to the variable number 56.

If you want to correlate parameters in different phases, you can connect them through the variables, so you could connect the b-lattice parameter in phase 2 to the b-lattice parameter in phase 1 by setting the both to variable number 34.

You can also use mathematical expressions, so you can set the occupancy of atom Na to @45 and the occupance of a different atom, K for example, to 1-@45 and then whenever one goes up, the other goes down.

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[Hao Lin]

Hi Prof. Billinge,

I see. Thanks so much

Hao

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[Hao Lin]

Hello Prof. Billinge,

I am using a C2/m cif file to fit my data. The cif file I downloaded from ICSD  has a bunch of sites but in literature they only give simplified sites.  Might i ask which i should use?