Dear Matthew, Thank you so much for your input. I followed your advice, and indeed the ratios of integrated chi(k) values between the polarized and isotropic cases matched reasonably well with the 3*cos^2(θ) values I calculated. To be exact, I integrated the scattering amplitude f(k) (i.e., the mag[feff] column in the path file) and took their ratios.

In the process, I noticed that the f(k) is slightly different for the same kind of paths. For example, there are two Ru-Ru single scattering paths at 3.10 and 3.54 angstroms, and below is the f(k) of the two paths (from a non-polarized FEFF calculation): [image: image.png] Is this discrepancy just an artifact of the FEFF calculation? While I'm not worried about such a small discrepancy for my project, this makes me wonder how exactly the FEFF calculates the effective scattering amplitudes and phases. While I will try to digest the FEFF user guide more, if you have any quick words of advice, I would appreciate it. Thank you very much, Soyoung On Mon, Feb 19, 2024 at 12:28 PM Matthew Newville < newvi...@cars.uchicago.edu> wrote: > Hi Soyoung, I would not place too much importance to the value of the > "Importance" factor ;) That is, it is a quick estimate of the importance of > a Path so that it might be filtered out. As you'll notice, the first path > always has > ZjQcmQRYFpfptBannerStart > This Message Is From an External Sender > This message came from outside your organization. > > ZjQcmQRYFpfptBannerEnd > Hi Soyoung, > > I would not place too much importance to the value of the "Importance" > factor ;) That is, it is a quick estimate of the importance of a Path so > that it might be filtered out. As you'll notice, the first path always > has an Importance factor of 100, making comparisons between calculations > difficult. > > If you want to check how the scattering amplitude varies with angle, say > to check how close it is to cosine-squared, I recommend reading in the Path > files and integrating the magnitude of chi(k). > > > > ------------------------------ > *From:* Ifeffit <ifeffit-boun...@millenia.cars.aps.anl.gov> on behalf of > Soyoung Kim <soy...@lbl.gov> > *Sent:* Thursday, February 15, 2024 3:01 PM > *To:* XAFS Analysis using Ifeffit <Ifeffit@millenia.cars.aps.anl.gov> > *Subject:* [Ifeffit] [IFEFFIT] Polarized FEFF calculation > > This Message Is From an External Sender > This message came from outside your organization. > > Dear XAFS community, > > I have a series of Ru K-edge data on a single-crystal RuO2 sample measured > at different incident X-ray angles. Because of the linear polarization of > X-rays, the EXAFS of this single-crystal sample depends on the X-ray angle. > I am trying to fit the four EXAFS spectra simultaneously with one set of > parameters to extract the deltaR and MSRD parameters of this sample. > > For oriented samples, N for a certain single scattering path is supposed > to be proportional to 3*cos^2(θ), where θ is the angle btwn the X-ray's > e-vector and the absorber-scatterer vector. Instead of manually calculating > the 3cos^2(θ) for all of the scattering paths in RuO2 (there are 7 single > and 3 multiple scattering paths that need to be included to achieve a good > fit with a reference RuO2 powder sample), I decided to use the polarization > card in my FEFF input. For example, for one of the X-ray angles, the > e-field vector would be (1, 0, 0), so I added the line "POLARIZATION 1 0 0" > in the FEFF input file. > > Running this input file gave me a list of paths that had different > importance values for each path compared to the non-polarized (isotropic) > calculation. *Since "importance" is the relative magnitude of each path's > scattering contribution (integration of the chi(k)), I thought that it > would be proportional to 3cos^2(θ).* That is, for path i from a FEFF > calculation for angle a, the "importance" (abbreviated as "Imp") of that > path would be: > Imp(a)_i = C(a) * Imp(iso)_i * 3cos^2(θ_i) > where C(a) is a constant for each angle that accounts for the fact that > importance values are relative (because it is scaled so that the first path > in the list has an importance of 100). > > Now, I wanted to check whether the polarized FEFF calculations really > follow this relationship underlined above. So, I tried manually calculating > the values of 3cos^2(θ) for two of the paths from the same polarized FEFF > calculation, then plug them into the above equation to get C(a). But, as > the table below shows, the C(a) values are not the same. FEFF 1 has a > disagreement that is small enough to ignore, but the disgareement of C(a) > values for The disagreement is small enough to ignore for FEFF 1, but for > FEFF 2 and 3 the disagreements are quite large. > [image: image.png] > *FEFF 1, 2, 3 designate individual polarized FEFF calculations. FEFF 1 was > with polarization vector = (1, 0, 0). FEFF 2 and 3 were with polarization > vector = (0.85, 1.13, 0). For this polarization, the two Ru sites gave > different lists of paths. > > I do think the qualitative trend of the "importance" values in the > polarized FEFF calculations is correct, and I can get a bad but > not-disastrous fit from simultaneously fitting the data from different > angles. However, the above analysis makes me wonder whether the > "importance" values from polarized FEFF are truly proportional to > 3cos^2(θ), and whether my fitting models for different angles, which I > derived from the polarized FEFF calculations, are correct. An alternative > would be to manually calculate 3cos^2(θ) for all the paths, but I'm not > sure how to calculate it for multiple scattering paths. > > One note, I am running the FEFF calculation with Larix to get the > importance values (labeled as "amp ratio" in the list.dat file, in the FEFF > output folder). I wonder if the default settings for getting these > amp ratios are not accurate enough for my purposes. It would be nice if I > could just pull out the 3cos^2(θ) terms from the FEFF calculations... > > Anyways, thank you very much for reading this rather lengthy question. > Hope it makes sense, and I would appreciate any help regarding this. > > Best, > Soyoung > > _______________________________________________ > Ifeffit mailing list > Ifeffit@millenia.cars.aps.anl.gov > https://urldefense.us/v3/__http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit__;!!G_uCfscf7eWS!d3iaM0LaHguTzEgY-JflrB_EKy_WaT_QTp-L6dyI90ixV9v_NIR02yqPQ5PadVV3-LmO1G3eYHcbOOPbOQ9Ej2b2w5rP6g$ > > Unsubscribe: > https://urldefense.us/v3/__http://millenia.cars.aps.anl.gov/mailman/options/ifeffit__;!!G_uCfscf7eWS!d3iaM0LaHguTzEgY-JflrB_EKy_WaT_QTp-L6dyI90ixV9v_NIR02yqPQ5PadVV3-LmO1G3eYHcbOOPbOQ9Ej2aG7EGo-g$ > >

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