[Ifeffit] Fwd: average first shell position and width

[Bruce Ravel]

Moneeb,

I'm in the middle of beam run, so I am forwarding this along to the
Ifeffit mailing list for commentary.

B


----------  Forwarded Message from Moneeb Shatnawi <Moneeb Shatnawi 
<mtshatnawi at pa.msu.edu>>  ----------

Subject: average first shell position and width
Date: Wednesday 27 June 2007
From: Moneeb Shatnawi <mtshatnawi at pa.msu.edu>
To: Bruce Ravel <bravel at anl.gov>

Dear Dr. Ravel,
 Hello,
 I am Moneeb Shatnawi from physics department at Michigan State University,

I have a PDF and XAFS data on GeSe system, and I would like to check if 
the PDF and XAFS results are consistent with each other in terms of the 
first PDF peak position and width.

The first PDF peak in this system is a mixed shell of Se-Se bonds as 
well as Ge-Se bonds.
The PDF data gave a width of the first PDF peak of about 0.06 A, and the 
XAFS data gave sigma^2 for Ge-Se bond is 0.006 A^2, and for Se-Se bond 
is 0.003 A^2.

How is sigma in XAFS results (I was using Artemis program) related to 
the width of the first PDF peak?

Also, when obtaining the XAFS fits to the data, I was using: Theory 
--->  first shell fit.
In this, I was giving r_eff for Se-Se bond to be 2.32 A and that for 
Ge-Se to be 2.368 A. Through the XAFS refinement, I obtained r, dr as 
well as r_eff.
which of these should be considered as the actual bond length (r or r_eff)?
and how are these related to the average position that I get from 
fitting the first PDF peak in this system?

I appreciate your help,
Thanks,
 Moneeb



-------------------------------------------------------

-- 
 Bruce Ravel  ---------------------------------------------- bravel at anl.gov

 Molecular Environmental Science Group, Building 203, Room E-165
 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007

 Argonne National Laboratory         phone and voice mail: (1) 630 252 5033
 Argonne IL 60439, USA                                fax: (1) 630 252 9793

 My homepage:    http://cars9.uchicago.edu/~ravel 
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/