Hi Mario, There are a couple of different ways to approach the kind of problem you describe, although you must be willing to guess at what the local environment looks like. For example, maybe the chemical composition tells you that you have an iron oxide. At a minimum, you could use Atoms to make a crystal structure for, say, hematite, and then only fit the nearest-neighbor paths, perhaps with an unknown coordination number. This can give you some information. Or, following the same example, maybe you think your material might be like a disordered hematite. Then you could try to fit the hematite structure out for several shells, but with free parameters to account for disorder (e.g. you could include vacancies). The key questions that you should not lose track of: --What would you like to know about your material? --What do you think your material might be like? I think sometimes people forget in particular about the first question. EXAFS doesn't answer generic questions very well ("tell me all about my sample"), but it often answers particular questions quite effectively ("are my iron atoms bonded to oxygen, or sulfur?"). So if you know what your particular questions are you've got a good chance of getting help using Bruce's and Matt's software. --Scott Calvin Sarah Lawrence College At 02:15 PM 3/28/2007, you wrote:

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Hi Bruce my name is Mario and I was just wondering if your program can fir the EXAFS spectra without any atomic positions. Obviously the answer is no if you use atoms to create the FEFF file but what does one do when we have a semi-crystalline material for which no one has attempted the fractional coordinates.

I mean the XRD pattern shows some crystalline but due to the high background I would think it would be very hard to do the Rietveld analysis.

So what can one do, can we fit the EXAFS spectra knowing only the chemical composition and perhaps the lattice geometry(orthorhombic or hexagonal)?

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