Just a little comment.
If you propagate uncertainties, there is mathematically no difference between the weightings and expected fits for k powers times chi, so differences will mainly be in correlated parameters. Without propagating uncertainties you can get different answers in different regions of k fitting but the differences do not reflect physical parameters.
--------------------------------------------------------------------------------------
Christopher Chantler, Professor, FAIP, Fellow American Physical Society
Editor-in-Chief, Radiation Physics and Chemistry
Chair, International IUCr Commission on XAFS; CIT, CCN
IPP, International Radiation Physics Society
School of Physics, University of Melbourne
Parkville Victoria 3010 Australia
+61-3-83445437 FAX +61-3-93474783
chantler@unimelb.edu.auhttps://owa.unimelb.edu.au/owa/redir.aspx?C=c7BoS0kVVkC1_S95-9x9l5cBu6YTjdAITgSrfUpfDAUV5oUH1LFYBcz08w8xvHMJoosZRdagfQM.&URL=mailto%3achantler%40unimelb.edu.au chantler@me.comhttps://owa.unimelb.edu.au/owa/redir.aspx?C=c7BoS0kVVkC1_S95-9x9l5cBu6YTjdAITgSrfUpfDAUV5oUH1LFYBcz08w8xvHMJoosZRdagfQM.&URL=mailto%3achantler%40me.com
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From: Ifeffit on behalf of ifeffit-request@millenia.cars.aps.anl.gov
Sent: Sunday, 29 August 2021 3:00 AM
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Subject: [EXT] Ifeffit Digest, Vol 222, Issue 6
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Today's Topics:
1. Manuscript comments regarding EXAFS modeling (Peng Liu)
2. Re: Manuscript comments regarding EXAFS modeling (Matthew Marcus)
----------------------------------------------------------------------
Message: 1
Date: Sat, 28 Aug 2021 10:40:37 +0800
From: Peng Liu
To: Ifeffit@millenia.cars.aps.anl.gov
Subject: [Ifeffit] Manuscript comments regarding EXAFS modeling
Message-ID:
Content-Type: text/plain; charset="utf-8"
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 (??) and coordination
number (CN), so any chosen value will be compensated by CN and ??. 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 (??). 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
