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