[Ifeffit] Fwd: from Rui Si at SSRF: help needed

[Bruce Ravel]

Hi Rui,

I am CCing my answer to you and to the Ifeffit Mailing List.  It's
always a good idea to use the mailing list as it greatly increases the
number of eyes that get to look at your question.  If you reply to
this, please do so via the mailing list.

In the PDF file you attached, you asked these two questions:

    (1) Why the second peak (ca. 3 Å) in experimental data is missing in
        the Co3O4 model?

I do not know anything about your sample, so this is a tough question.
Are you certain of its phase purity?  Could there be another form of
cobalt oxide present in the sample?

    (2) Why need to add the “shift vector” suggested by Artemis?
        Actually, no action is required and the software change the Co
        core from 0.125, 0.125, 0.125 to 0.5 0.5 0.5, and keep the shift
        vector as 0 0 0.

The purpose of the shift vector is explained here:

 
http://bruceravel.github.io/demeter/artug/atoms/space.html#multipleoriginsandtheshiftkeyword

In the case of the CIF file you attached, the shift vecotr does not
seem required.  The list of atomic coordinates without the shift
vecotr looks right to me.

B



-------- Original Message --------
Subject: 	from Rui Si at SSRF: help needed
Date: 	Tue, 15 Jul 2014 07:33:31 +0000
From: 	司锐 <sirui at sinap.ac.cn>
To: 	bravel at bnl.gov <bravel at bnl.gov>



Hi Bruce,

Here, I have a question needs your help on the EXAFS fittings.

When I tried to fit the Co3O4 standard (cif and apj file attached),
there was a "shift vector" problem, which has been resulted in the
mismatch between experimental data and theoretic model. Please see the
details in the attachment.

I am not familiar with crystal models, and thus I cannot find the key.
Could you please help me?

Many thanks!

Best,

Rui

----------------------------------------------------------
Dr. Rui Si
Shanghai Institute of Applied Physics, Chinese Academy Sciences
Shanghai Synchrotron Radiation Facility
Address:
239 Zhangheng Rd, Pudong District
Shanghai 201204, China
E-mail: sirui at sinap.ac.cn
Tel: (86)21-33932079
Cell:(86)13301753969


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