Was there a standard measured that's chemically similar to the unknown?
If so, S0^2 could be set by requiring that the CN of the standard be
what it's known to be. Often, the dσ² is mostly relevant in terms of
differences or changes so an error in the absolute value isn't very
important. If valence and ligands make such a big difference then it
would be impossible to measure CNs on samples for which no
extremely-similar model compounds are available.
Also, it's never been clear to me how doing the fit at three different
k-powers is better than doing it at just one intermediate value. The
idea that it somehow gets you low-k and high-k information in a better
way seems like an attempt to pull out more independent data points than
actually exist. OTOH, proving that you get the same answers, within
error bars, at different exponents would be a confidence-builder.
mam
On 8/27/2021 7:40 PM, Peng Liu 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
<https://scholar.google.com/citations?user=qUtyvokAAAAJ&hl=en>
http://grzy.cug.edu.cn/049121/zh_CN/index.htm
<http://grzy.cug.edu.cn/049121/zh_CN/index.htm>
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