Hi Fan,

On Fri, May 12, 2023 at 9:56 AM <dxfan@post.kek.jp> 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

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