Re: [Ifeffit] iron carbide fitting with Artemis

Hello Mike, Thank you very much for your help. I have a question about combining different atoms in a shell. For example, in the Fe5C2 model, ATOMS * this list contains 221 atoms * x y z ipot tag distance 0.00000 0.00000 0.00000 0 Fe1 0.00000 -0.19385 1.76888 -0.78107 4 C1.1 1.94335 -0.19385 -0.94552 1.72493 4 C1.2 1.97661 If I am going to combine C1.1 and C1.2, shall I set them the cartisian coordinate as in FEFF file? ATOMS * this list contains 221 atoms * x y z ipot tag distance 0.00000 0.00000 0.00000 0 Fe1 0.00000 0.00000 0.00000 1.94335 4 C1.1 1.94335 Thanks a lot for your help again! Best, Yunyun On Thu, Oct 26, 2017 at 4:40 PM, Mike Massey wrote:

I definitely recommend combining multiple atoms of similar distances into the same path. That's what you end up with anyway if you use multiple paths, with a lot more potential problems in the software.

Sometimes it is beneficial to split a shell of of atoms into two, to capture some physical behavior (for example, 2 atoms at 3 Angstroms and 4 atoms at 3.3 Angstroms, instead of one very disordered shell of 6 atoms at 3.2 Angstroms).

Depending on your data quality, I recommend building a fitting model with maybe 2-8 total "shells" of atoms at different distances.

Mike

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On Oct 26, 2017, at 12:52 PM, Yunyun Zhou wrote:

Hello All,

I am having trouble fitting my sample with both Fe5C2 and Fe3O4 as standards. Hopefully somebody could help me out and I really appreciate it.

My iron sample was mainly iron carbide in the core and iron oxide on the shell. Fe5C2 has a monoclinic structure and generated complicated FEFF paths. Many of the paths have similar distances. I have found some paper reported their results as follows, which apparently combined several paths together and assume they have similar path length. My first question is does someone know how they did it? It seems that combing similar paths makes fitting much easier, but I am not sure whether this is a correct way to do the fitting.

My second question is regarding fitting with the two combined models of Fe5C2 and Fe3O4. I haven't fit with two models before. Is it just like what I did in the attached Artemis file? Shall there be any restrictions between the two models and do I have to fix some of the parameters?

Thank you very much in advance for your help!

Best,

Yunyun Zhou

Fe5C2 FEff paths:

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