Hi Fan,
On Fri, May 12, 2023 at 9:56 AM
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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