Hi Ava, I think you'll have to give us more details about what you have done. The figures you show are all in R-space, so after at least some processing... So, yes, project files and/or scripts would be helpful. Yes, there can be subtle changes in the background subtraction (and in the normalization process too) between Larch and Ifeffit/Athena/Artemis.
By default, Artemis uses Feff 6.10 and Larch uses Feff 8. For the C K edge, that could have a noticeable difference, especially in the placing of the k=0 value, though I do not know how big that effect would be for C (graphite?). But also, Artemis and Larch can both read the inputs from the other calculations: it might be that this is what you have done to make the plots, but that wasn't 100% clear to me. On Mon, Oct 16, 2023 at 2:08 PM Ava Rajh <ava.r...@ijs.si> wrote: > Dear all! > > I haven't been able to find a similar question/issue in the previous > threads, so I hope someone can help me figure out what is going on. > > I am trying to fit a Carbon EXAFS spectra, using graphite as a model. I > am first focusing on just the first two single scattering paths, so I > calculated the theoretical paths with FEFF in Larch and tried using them > to fit the spectra. I was consistently getting slightly lower distances > than expected, but otherwise an OK fit. > > The issue is, I tried to compare the analysis with a colleague who is > using Athena. At first glance the EXAFS spectra, using the exact same > parameters, looked very similar (but not exactly the exactly the same, > this I attributed to Larch using a different autobk procedure). I would > have however expected the theoretical paths to match exactly, if they > were calculated and plotted with the same parameters. But they were also > slightly different. I then downloaded Athena and spent time trying to > find where the differences come from. If I compare the first two > calculated shells from Larch with the ones from Athena, with exactly the > same set of test parameters (S02 = 1, E0 = 0, dr1 = 0, s2_1 = 0, dr2 = > 0, s2_2 = 0), the resulting models do not match. I made sure the paths > are calculated from the came .cif file in both cases, use FEFF6, have > the same calculated reference distances, same FT... > > So, my main question is, am I missing something important in regards to > calculations, why would the calculated paths be different and which one > would be the "correct" one to use for the fit? And the other question > would be about the fact that EXAFS spectra of experimental data look > slightly different using Larch and Athena, am I right in disregarding > this, or should I dig deeper and find the source of discrepancy? > > I am enclosing a plot of just the calculated first two shells from > Athena and Larch (FT: kmin = 2, kmax = 7.5, Fittting in R space, kw = > 3, kWindow = Hanning, dk = 1.0, Rmin = 0.6, Rmax = 2.1) along with the > cif file I ended up using for testing the differences. If it would be > helpful, I can also provide the project files and larch script I used > for the dataset, but I am mainly interested in understanding the > differences seen in the theoretical parts first. I tested this using > Larch v 0.9.72 and Demeter 0.9.26 > > Thank you ver much for the help, and If I need to provide any additional > info please let me know. > kind regards, Ava > > -- > Ava Rajh_______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit > Unsubscribe: http://millenia.cars.aps.anl.gov/mailman/options/ifeffit > --Matt
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