Number of atoms in cif file and PDFgui are not matching & Finding coherence length

[Arya Sukumaran]

Hi all,
1. I am working on fitting PDF data for Li argyrodite with aliovalent substitution. As a result of aliovalent substitution, the number of Li atoms increases in the substituted samples compared to the pristine one.

For some composition the number of Li shown in PDFgui is matching with that of stoichiometry, and others are not.

Has anyone faced similar issue? Or has any idea what could be the reason?

2. Could you please guide me on how to determine the coherence length of crystalline materials using PDFgui? Or could you provide any reference to understand it?
Thank you.

[Simon Billinge]

Daer Arya,  Thanks for the question.

Please could you share a bit more information to halp us debug your situation.

1. please could you reproduce some of hte steps you used to generate your PDFgui phase?  Did you load a cif file?  Did you expand using space-group, etc?
2. please could you maybe share a couple of screenshots of what you are seeing in the PDFgui interface when it working and when it is not?

This would help enormously.

For the correlation length, you have a number of options.  One of the best explanations of this is in Qiu et al, 10.1103/PhysRevLett.94.177203

On Mon, May 5, 2025 at 12:04 AM Arya Sukumaran <aryasuk...@gmail.com> wrote:

Hi all, 1. I am working on fitting PDF data for Li argyrodite with aliovalent substitution. As a result of aliovalent substitution, the number of Li atoms increases in the substituted samples compared to the pristine one. For some composition

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Simon Billinge

Professor, 

Department of Applied Physics and Applied Mathematics

Columbia University

[Arya Sukumaran]

Dear Prof. Billinge,

Thank you for the support. 

We have loaded the CIF file in PDFgui. I am attaching the PPT with screenshots of the PDFgui interface when the number of Li atoms is not matching and when it is matching with the stoichiometry.

Thank you