Re: [Ifeffit] [Attachment Removed] Re: Low amplitude chi signal of first shell calculated by FEFF
Hi Fan,
If you included an attachment, I did not see it. If so, can you send it
some other way?
I would not expect that the Sr K-edge of SrTiO3 needs much playing around
with parameters in the feff.inp file prior to running Feff. I would
advise against doing that unless you know what you are doing. Don't set Vi
to be below 0.
I would be more inclined to believe that the data treatment had problems or
that the use of the feff paths had problems. Without knowing what you
did, it is very hard to speculate what might be going wrong.
On Tue, May 23, 2023 at 9:38 PM Dongxiao
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Hello, Matt, cc: who is interested,
Thank you very much for your reply.
The low amplitude chi signal is common when I calculated the A site EXAFS signal of perovskite structure.
Especially the chi signal of first single scattering path (A-O) is unreasonable low.
In my case (Sr K-edge EXAFS of SrTiO3), the intensity of calculated chi is smaller than the low-temperature experimental chi.
I have been struggling with this problem for some time. I am looking forward to somebody who can give me some advice..
I attached the related files for your check.
I try to vary Vr and Vi value and want to see how the amplitude change.
If set the Vi to negative, it indeed can increase the amplitude, but I don’t know if it is proper.
Maybe the problem is caused by the bad muffin-tin potential, but I don’t know how to improve it.
Can you give me some advice?
Best regards,
Fan
-----Original Message-----
Matt Newville https://www.mail-archive.com/search?l=ifeffit@millenia.cars.aps.anl.gov&q=from:%22Matt+Newville%22 Fri, 12 May 2023 14:25:36 -0700 https://www.mail-archive.com/search?l=ifeffit@millenia.cars.aps.anl.gov&q=date:20230512
Hi Fan,
On Fri, May 12, 2023 at 9:56 AM
wrote: Hi, All
The problem I meet is the low amplitude chi signal of first shell
calculated by FEFF.
The consequence of the fitting is large value of SO2 (1.5-2.0), which is
quite unacceptable.
I tried to fit the dataset measured by different people at different
beamline, the consequence is same.
My data is T-dependent Sr K-edge EXAFS of SrTiO3, path file generated by
FEFF10, fitting process by Larch+python.
By check the email list, it seems the long shell distance (2.7 A) is the
origin of the problem. I am not sure for that.
I also try to vary the Vi value to improve the amplitude, the change is
small.
Can any body give me some advice?
I would not expect that a Sr-O distance of 2.7 to 2.8Ang would cause an
amplitude problem. I would tend to expect that being off by a factor of 2
would
imply normalization issues. You could try to vary Vi, but I would not
guess that you need to do that. Why do you set Vi to 2 (eV)?
Do you have data and/or analysis steps (script or Larch session file) you
can share?
Best regards,
Fan
My feff.inp file is like:
--------------------------------------------
* This feff8 file was generated by Demeter 0.9.26
* Demeter written by and copyright (c) Bruce Ravel, 2006-2019
* --*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--
* space = 221
* a = 3.90500 b = 3.90500 c = 3.90500
* alpha = 90.00000 beta = 90.00000 gamma = 90.00000
* rmax = 9.00000 core = Sr
* polarization = 0 0 0
* shift = 0 0 0
* atoms
* # el. x y z tag
* Sr 0.00000 0.00000 0.00000 Sr
* Ti 0.50000 0.50000 0.50000 Ti
* O 0.00000 0.50000 0.50000 O
* --*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--
* --*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--
* total mu*x=1: 32.298 microns, unit edge step: 44.289 microns
* specific gravity: 5.118
* --*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--
* normalization correction: 0.00029 ang^2
* --*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--*--
* Sr K edge energy = 16105 eV
EDGE K
S02 1.0
* pot xsph fms paths genfmt ff2chi
CONTROL 1 1 1 1 1 1
PRINT 1 0 0 0 0 3
* ixc [ Vr Vi ] *** ixc=0 means to use Hedin-Lundqvist
EXCHANGE 0 2 1 -1
*** Radius for self-consistent pots (2 shells is a good choice)
* r_scf [ l_scf n_scf ca ] *** l_scf = 0 for a solid, 1 for
a molecule
SCF 7 0 100 0.1 1
* kmax [ delta_k delta_e ] *** Upper limit of XANES
calculation.
* XANES 4.0
* r_fms l_fms *** Radius for Full Mult. Scatt. l_fms = 0
for a solid, 1 for a molecule
* FMS 16.77392 0
* emin emax eimag *** Energy grid over which to calculate DOS
functions
* LDOS -30 20 0.1
*** for EXAFS: RPATH 5.0 and uncomment the EXAFS card
CRITERIA 0 0
* POLARIZATION 0 0 0
COREHOLE FSR
RPATH 7.0
LDOS -30 20 0.1
EXAFS 20.0
--Matt
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Matt Newville