Hi Peng, This will echo much of what Matthew Marcus wrote:
For comment 1 on S02, picking a value of 0.85 seems reasonable. I think the reviewer is asking you to explain how you got that value. Saying something like "we chose that value so that the data from a simple metal foil (or simple metal oxide, etc) gave the expected first shell coordination number" should be enough. Typically, S02 is determined once for a given set of data with the same beamline conditions and *not* varying from sample to sample. For comment 2 on correlation, I would emphasize that N and sigma2 are well-known to be correlated and that this correlation cannot be eliminated. The correlation is "managed" as all correlations are managed - by a statistical analysis of that correlation. The uncertainties reported for all fitting variables always take those correlations into account. That is just a normal part of the analysis. There is a common misconception that using multiple k-weights "eliminates" correlations between variables. It does not. It is available in ifeffit/artemis/larch to try to help find more robust solutions. In my experience, simultaneously using k-weights of 1, 2, and 3 does not actually givr very results compared to using a k-weight of 2 or 3 alone, though I'm willing to believe that there are cases where it can help find a solution for a fit with both low-Z and high-Z scatterers. That is, using multiple k-weights is a fine thing to do but it does not lower correlations between N and sigma2 (or E0 and R) by very much. Cheers, On Fri, Aug 27, 2021 at 7:41 PM Peng Liu <liupeng5...@gmail.com> wrote: > Dear Ifeffit members, > > I received the following two comments. > > " > Comment 1: Authors have fixed the amplitude reduction factor (SO2) to a > fixed value (0.85). This factor is specific to particular chemical compound > and sample preparation and quality (mostly homogeneity), measurement method > (e.g. absorption, fluorescence). Authors can find in literature [e.g. > Rehr2000] that SO2 for ideal samples (having no other effects) represent > multielectron effects, which by definition depend on valence and ligands. > Even more, SO2 is correlated with Debye-Waller factor (σ²) and coordination > number (CN), so any chosen value will be compensated by CN and σ². As > coordination numbers are used as quantitative indicators in discussion and > following conclusions. I would request to clarify the selection criteria > for SO2 values and advise to revise this approach (i.e. not to fix SO2 as > the same value for all samples). I do not expect drastic changes in > obtained CN values, but this should be tested. > > Comment 2: As I mentioned previously, coordination number (CN) is > correlated with Debye-Waller factor (σ²). My question is: how this > correlation is managed (eliminated)? Most probably (in FEFFIT) this is done > by using 3 separate values for n (1,2,3), where n is a power in expression > chi(k)*(k^n). > " > I used Artemis for the calculation. 1) Because S02 and CN are > multiplication relations in the EXAFS equation, as we usually do, we fixed > S02 to obtain CN for unknown samples. 2) there are outputs regarding the > correlation between different fitting parameters from Artemis. Is there a > way to manage or eliminate the correlation as the reviewer mentioned using > Artemis or Larch? > > If you also could give me some suggestions to answer the comments, that > would also be greatly appreciated. > > -- > Best Regards, > > Peng Liu > > School of Environmental Studies > > China University of Geosciences, Wuhan, Hubei Province, PR China > > https://scholar.google.com/citations?user=qUtyvokAAAAJ&hl=en > http://grzy.cug.edu.cn/049121/zh_CN/index.htm > _______________________________________________ > 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 >
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