Re: [Ifeffit] running ifeffit-1.2.11 under 64-bit Windows 7

2012-03-07 Thread Dr. Dariusz A. Zając

Dear Sameh,
I use also 64 bit Win7 and I do not observe any strange behaviour. All 
results I got are reasonable, and fitting with different models/starting 
parameters gives me the same final results (for the same sample, of 
course). More, I can compare results under Win Xp (old computer) with 
results under Win7, and I see very good agreement.
I run Ifeffit package directly under Win7, I didn't need to run in Win 
XP mode.

U use also Jfeff which runs OK

maybe you can tell something more about this strange manner and about 
your sample/results

best regards

W dniu 12-03-07 11:11, sameh pisze:


I have a new computer with 64-bit windows7. I have noticed that 
Artemis is running in a strange manner, it never produces the same 
results when the same data is fitted twice.

I have uninstalled and then reinstalled the whole (ifeffit-1.2.11) 
package with the compatibility wizard which suggested to run the 
package in compatible mode to windows XP. After doing so, any of the 
programs is not running at all.

My old laptop was 32-bit which runs 32-bit windows 7 and the 
ifeffit-1.2.11 package was running normally with this computer.

Thank you very much and best regards

Sameh Ibrahim Ahmed

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Re: [Ifeffit] Crystallographic data for V(CO)6

2012-03-07 Thread Christopher Patridge

You do really not need exact parameters which can is helpful in EXAFS.  Can
you find any references on the V-C bond length?  Since CO is linear, the
V-O and V-C-O scattering should be possible to roughly establish.  I think
a number of general inorganic textbooks might have information such as this
on metal carbonyl bonding.  If the lattice parameters are not too
different, start with simple octahedral geometry and the quick first shell
fit using V-C bond length.

buena salud,

Chris Patridge

On Wed, Mar 7, 2012 at 1:39 PM, Ismael Graff wrote:

 Dear XAS fellows:

 I have to fit EXAFS data of a nanoparticle colloidal suspension. TEM and
 NMR data indicate that I have nanoparticles of V(CO)_6 (vanadium
 hexacarbonyl). The system is orthorhombic, space group Pnma (Nr. 62), and
 I know the nominal values for the lattice parameters. However, I need the
 different atomic positions/coordinates to enter in ATOMS. Usually I get
 such information from a CIF (Crystallographic Information File) card. But
 in this case, I didn´t find it in the open data banks.

 Is anyone out there that could help me?

 Cheers, Ismael.

 PS: A similar structure/material would also help (like Mo(CO)_6)!

 *Ismael Leandro Graff  *
 *  *
 * Universidade Federal do Paraná   *
 * Departamento de Física, CP 19044 *
 * 81531-990, Curitiba, Brazil. *
 * Tel (office): +55 41 3361 3278   *
 * Tel (Lab): +55 41 3361 3427  *
 * Fax: +55 41 3361 3418*
 *  *

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Christopher J. Patridge PhD.
Contact: (315)-529-0501
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[Ifeffit] appropriatness of feff model when central atom is not embedded (or only 1 layer embedded)

2012-03-07 Thread Andrea L Foster
Hello All,  can someone please help with this:

(1) feff requires that the adsorbing atom be embedded  (that is, 
surrounded by) other atoms in order to calculate potentials correctly, but 
how deeply does the atom need to be embedded? 

For example, if  I construct a model of an adsorbate on a mineral surface, 
where that adsorbate has a full complement of 1st shell coordinating OH, 
O, and H2O groups as appropriate, but if I do not include all the 
uncoordinated f water atoms that would be nearby (so that I essentially 
have a surface in vacuum), will the potentials for my central atom be 
calculated correctly (or correctly enough for use in IFEFFIT)?

a more specific example: the AsO4 tetrahedron bonded to the goethite 
surface, which is made of octahedrally-coordinated iron.  The arsenate 
bonds to the goethite  by sharing 1 edge of the tetrahedron with the 
apices of 2 adjacent Fe octahedra.

a related question that comes to mind: if I just wanted to see the signal 
from the 2 adjacent Fe atoms, could I create a perfectly useable FEFF 
model (for IFEFFIT) by limiting my calculations to the small cluster of 1 
arsenate tetrahedron and 2 Fe octahedra?

thanks, andrea

Andrea L. Foster, Ph.D.
345 Middlfield Rd., MS 901
Menlo Park, CA 94025
T: 650-329-5437
F: 650-329-5491

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Re: [Ifeffit] inquire for the EXAFS of the mixture of species

2012-03-07 Thread Dr. Dariusz A. Zając

Hi winejia,
it is trivial but at the same time hard problem to solve.
There are 2 ways: using Athena and using Artemis
Using Athena you have measured your sample and all possible references. 
The result comes from the fit of the linear combination of your references.
Using Artemis is similar but instead of measured references you create  
models (FEFF cards) from known structures and than fit to your 
experimental data.
For sure you will find some more tricks in the archive of this mailing 

good luck

W dniu 12-03-08 05:47, winejar8324 pisze:

Hello everyone,
I have a puzzle during analyzing of my EXAFS data. can someone please 
help me:
I have a set of EXAFS data on solution sample at different pH. I wish 
to extract  the structure information from the EXAFS region to accont 
for the reaction machanism. However, there are several 
configurations(as indicated by XANES) and species(as indicated by 
thermodynamics caculation) in solution due to the metal-Ligand complex 
How can i obtain the structure information about this complex system 
from the EXAFS data?

Thanks, winejia

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