[Ifeffit] Fwd: regading feff input file of sorbed species

[Bruce Ravel]

Hi everyone,

Below is an email I received this morning.  I thought I would pass it along to 
the mailing list.  I know that some of you work on projects very close to this 
fellow's question and thought he would benefit by the wisdom of the masses.

Hi Sumit,

A few pointers:

 * There is a wealth of information about Feff and XAFS analysis at 
http://xafs.org

 * I strongly encourage you to join and follow this mailing list.  I explain 
the many benefits of the mailing list and offer some advice on using it 
effectively at this page: 
http://cars9.uchicago.edu/ifeffit/BruceRavel/FormLetters/HelpRequest

As for your question -- there are a number of approaches to the problem of 
sorbed species that have been adopted by folks working both catalysis, in 
environmental science, and elsewhere.  Obviously, sorbed species are a very 
important topic in many fields and XAS is very attractive for learning 
something about them.  You would be very well served by examining the very 
large body of published literature on this topic.  Much of that work has been 
done by people who read this mailing list -- I am hoping some of them will 
speak up.

As I said, there are a number of ways to approach the problem.  One fairly 
simple way is to run atoms on the substrate crystal and then "cut" the 
resulting cluster to "expose" the surface.  What does this mean?  The simplest 
case is to "expose" a (001) surface by simply deleting all atoms from the Feff 
input file with a positive value for the Z coordinate (assuming, of course, 
that the crystal is of an orthogonal type -- this "cutting" trick is a bit 
trickier for other cystal types).  Then simply decorate the atoms list with 
the absorber by placing at coordinates relative to the "exposed" surface that 
is a plausible place to find that atom.  Be sure you set the POTENTIALS list 
on the Feff input file correctly to account for the newly introduced absorber.  
This is explained in the Feff documentation and ion several places at 
xafs.org.

Hope that helps,
B 


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On Tuesday 12 January 2010, 08:21:04 am, sumitk at barc.gov.in wrote:



Dear Sir,

This is in regrad to the problem in making the FEFF input file for the Eu 
species sorbed on the the alumina surface.

I am Sumit Kumar, Working as Reseach Scholar In Indian Nuclear Establishment. 
Recenrly I have carried out Eu-L3 EXAFs experiemnt at Elettra Synchrotron 
EXAFS 
beamline for delineating Eu species sorbed on alumina and other clay surfaces 
under different experiemntal/environmental conditions. 

As I understand for FeFf input file ATOMS SOFTWARE can be used, but as my 
species are just sorbed/chemical bonded on the surface, I can not take Eu as 
part of the bulk and then using ATOMS will be not be correct. 
I need your suggestion in this regard. Pl. suggest how to make the FEFF input 
file in this case. My problem is similar to one of yours paper sumitted to 
Geochimica Cosmochimica acta(Zn on Rutile).If you could send FEFF input file 
file for that work or similar other FEFF input file, it will be of much help 
to 
me.

With Regards,
Sumit Kumar
Radiochemistry Division
Bhabha Atomic Research Centre, Mumbai, India


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