[Ifeffit] Question on GDS values: amp

[Dominik Samuelis]

Dear Nic,

I've had a short look into your Artemis file. First of all, it seems 
that something's wrong with the Gd2O3 structure data in your feff.inp.

Running feff on your feff.inp gives this error:

  Feff 8.40
  ...
  WARNING:  TWO ATOMS VERY CLOSE TOGETHER.  CHECK INPUT.
  atoms        8      14
     8  2.24848E+00  2.70250E+00  0.00000E+00
    14  2.47549E+00  2.70250E+00  0.00000E+00
  Run continues in case you really meant it.
  WARNING:  TWO ATOMS VERY CLOSE TOGETHER.  CHECK INPUT.
  atoms        9      15
     9 -2.24848E+00 -2.70250E+00  0.00000E+00
    15 -2.47549E+00 -2.70250E+00  0.00000E+00
  Run continues in case you really meant it.
[...]

It seems that all your "Gd2" atoms have a duplicate in your "Gd3" atoms, 
shifted only by ~0.2 angstroms in either x,y, or z direction.

Looking further at your feff.inp, already your ATOMS input somehow looks 
broken:

(your ATOMS list)
  *   Gd    0.25000    0.25000    0.25000  Gd1           1.00000
  *   Gd    0.02100    0.00000    0.25000  Gd2           1.00000
  *   Gd    0.54200    0.00000    0.25000  Gd3           1.00000
  *   O     0.12500    0.12500    0.37500  O1            1.00000
  *   O     0.12500    0.37500    0.37500  O2

(my list, cif file from ICSD, Shuenn et al., J. Chin. Chem. Soc. 57 
(2010), 938)

Gd	0.25	0.25	0.25	Gd1	1.000		* (8b position)
O	0.3904	0.1513	0.379	O1	1.000		* (48e position)
Gd	0.9710	0	0.25	Gd2	1.000		* (24d position)

Using this crystal data, I was able to fit your data reasonably well 
(didn't tweak to make the fit perfect though...) - see attached file!

I've also attached the .cif file that I've used, in case you want to 
compare with yours.

BTW, enot values of >20 eV shouldn't really happen in any fit.

Best regards,
Dominik


On 02.08.2011 04:42, Nicholas.Tse at csiro.au wrote:
> Thank you all the suggestions.
>
> I believe the ATOM model used is representative of what it should be. I generated the FEFF file from the CIF file from the American Mineralogist X'stal DB. The generated FEFF has the edge L3 that should be fine. A simple summation of the scatter paths does roughly produce the pattern for the sample, except for the amplitudes.
>
> The enot was found to be 53.8995 +/- 2.7632.
>
> I have also included the .prj and .apj files for your inspection.
>
> Regards,
>
> Nic
>
>
>
>
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-- 
Dr. Dominik Samuelis
d.samuelis at fkf.mpg.de
Max-Planck-Institut für Festkörperforschung
Max Planck Institute for Solid State Research
Heisenbergstr. 1
70569 Stuttgart
Germany
Phone +49-711-689-1769
Fax   +49-711-689-1722
Web   http://www.fkf.mpg.de/maier/
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