[Ifeffit] need help to get better fitting

[Yun Xu]

*Hello, This is Mia From Clemson University.*
*I have problem with my fitting, this has bothered me for long time.*
*So the thing is I use Fe metal foil as reference, and I was able to get
S02 from fitting the Fe metal foil XAS as seen in the attached file
Fe_metal foil fit.*
*Then I used this S02 value to fit the Fe_kedge exafs data of Hollandite
sample, Cs1.33Fe1.33Ti6.67O16. The hollandite crystal structure cif file is
also attached as hollandite.cif. Fe and Ti sit in the six oxygen
coordinated octahedral. the crystal structure is shown in the attached
figure as hollandite.jpg. (neglect the color of octahedra) This cif file is
the original structure without dopant as BaTi8O16 (I4/m space group). so I
set the core atom as Fe in the Feff, and assume second and third shell as
Ti, in the DFT calculation, Fe octahedra tend to have a Ti octahedra as
neighbor rather than a Fe ocatahedra. *
*I've also attached my artemis file to see anybody could help me get  a
better fitting. I just need to fit the range up 3.5A which includes the
first oxygen shell and Two Ti shell.*
*A specific question is I always get negative S02 value, can any body tell
me what I should do if I get negative S02.*
*Thank you very much*
*Mia*
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