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<DIV><FONT size=4>Dear Scott,</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>Thanks for your explaination. All the samples were measured at
77K using a homemade <FONT face=宋体><FONT style="FONT-SIZE: 12pt">cryogenic box.
I will try to do the Hamilton test according to your
book.</FONT></FONT></FONT></DIV>
<DIV><FONT size=3 face=宋体></FONT> </DIV>
<DIV><FONT size=3 face=宋体></FONT> </DIV>
<DIV><FONT size=3 face=宋体>Best,</FONT></DIV>
<DIV><FONT size=3 face=宋体></FONT> </DIV>
<DIV><FONT size=3 face=宋体>Shaofeng</FONT></DIV>
<DIV><FONT size=3 face=宋体></FONT> </DIV>
<DIV> </DIV>
<DIV
style="FONT-FAMILY: 'Century'; COLOR: #000000; FONT-SIZE: 14pt">--------------------------------------<BR>Shaofeng
Wang, Ph.D of Geochemistry<BR>Environmental Molecular Science Group<BR>Institute
of Applied Ecology, Chinese Academy of Sciences<BR>Shenyang, 110016,
China<BR>wangshaofeng@iae.ac.cn<BR>www.iae.cas.cn<BR><BR></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none">
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<DIV> </DIV>
<DIV style="BACKGROUND: #f5f5f5">
<DIV style="font-color: black"><B>From:</B> <A title=scalvin@sarahlawrence.edu
href="mailto:scalvin@sarahlawrence.edu">Scott Calvin</A> </DIV>
<DIV><B>Sent:</B> Thursday, January 05, 2017 11:50 AM</DIV>
<DIV><B>To:</B> <A title=ifeffit@millenia.cars.aps.anl.gov
href="mailto:ifeffit@millenia.cars.aps.anl.gov">XAFS Analysis using Ifeffit</A>
</DIV>
<DIV><B>Cc:</B> <A title=wangshaofeng@iae.ac.cn
href="mailto:wangshaofeng@iae.ac.cn">Shaofeng Wang</A> </DIV>
<DIV><B>Subject:</B> Fwd: about sigma2 for exafs fitting</DIV></DIV></DIV>
<DIV> </DIV></DIV>
<DIV
style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none">Shaofeng
has given me permission to repost her question here on the ifeffit mailing list.
It is quoted below my response.
<DIV> </DIV>
<DIV>Dear Shaofeng,</DIV>
<DIV> </DIV>
<DIV>As Bruce and I said before, a sigma2 of 0.0007 A^2 is not impossible,
although it indicates less disorder than is <I>typically</I> present. Your
attached table does seem to show some improvement by using the model from the
hydrogen-containing structure as compared to the arsenate. A more rigorous test
for statistical improvement can be conducted using the Hamilton test (you
mentioned you’ve consulted <I>XAFS for Everyone</I>; full details of the
Hamilton test are given there). </DIV>
<DIV> </DIV>
<DIV>It’s also encouraging that the uncertainties on your sigma2 determinations
using the hydrogen-containing model are quite small; it appears that the fit is
not getting confused by correlations even though it’s fitting both coordination
number and sigma2, as that would generally also cause high uncertainties in the
correlated parameters.</DIV>
<DIV> </DIV>
<DIV>Is such a stiff sigma2 reasonable <I>in this case</I>? I have no idea. I
just don’t know enough about this particular system; perhaps someone else on the
list does. Oh, and one other question—was the data collected at room
temperature? If it were collected at cryogenic temperatures, that would tend to
reduce thermal disorder and thus lower sigma2’s.</DIV>
<DIV> </DIV>
<DIV>Even if no one on the list has insight in to this particular system, anyone
have good published examples of room-temperature systems with sigma2’s <
0.001? It might help Shaofeng with her referee…</DIV>
<DIV> </DIV>
<DIV>Best,</DIV>
<DIV> </DIV>
<DIV>Scott Calvin</DIV>
<DIV>Lehman College of the City University of New York</DIV>
<DIV> </DIV>
<DIV>P. S. I certainly hope no reviewer is using the “typical values” I provide
for parameters in <I>XAFS for Everyone</I> as rigid criteria for rejecting
results! It is most certainly not the way I use them in the book. Some systems
actually <I>are</I> atypical!<BR>
<DIV><BR>
<BLOCKQUOTE type="cite">
<DIV>Begin forwarded message:</DIV>
<DIV> </DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif; COLOR: "><B>From:
</B></SPAN><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif">Shaofeng
Wang <<A
href="mailto:wangshaofeng@iae.ac.cn">wangshaofeng@iae.ac.cn</A>><BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif; COLOR: "><B>Subject:
</B></SPAN><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif"><B>about
sigma2 for exafs fitting</B><BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif; COLOR: "><B>Date:
</B></SPAN><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif">January
4, 2017 at 8:31:33 PM CST<BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif; COLOR: "><B>To:
</B></SPAN><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif"><<A
href="mailto:scalvin@sarahlawrence.edu">scalvin@sarahlawrence.edu</A>><BR></SPAN></DIV>
<DIV style="MARGIN: 0px"><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif; COLOR: "><B>Reply-To:
</B></SPAN><SPAN
style="FONT-FAMILY: -webkit-system-font, helvetica neue, helvetica, sans-serif">Shaofeng
Wang <<A
href="mailto:wangshaofeng@iae.ac.cn">wangshaofeng@iae.ac.cn</A>><BR></SPAN></DIV>
<DIV> </DIV>
<DIV>
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<DIV style="FONT-FAMILY: century; FONT-SIZE: 14pt">
<DIV><FONT size=4>Dear Dr. Calvin,</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>I am a research from China. I know you are an expert on XAFS
analysis. So I write this letter to you for some xafs analysisi problem.<SPAN
class=Apple-converted-space> </SPAN></FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>Recently, I am attempting to study the incorporation of
arsenate into the barite structure. To investigate the species of arsenate in
barite, I fitted the exafs data using Ba3(AsO4)2 and a dft optimized structure
with HAsO<SUB>4<SPAN
class=Apple-converted-space> </SPAN></SUB>incorporated in barite
supercell (configuration C2), respectively and got some results. Please see
the attached table. Smaller reduced chi2 and R-factor were obtained by using
configuration C2 as the initial model. Does this mean the species of arsenate
in barite is more likely to be HAsO<SUB>4</SUB><SUB></SUB><SUP>2-</SUP><SPAN
class=Apple-converted-space> </SPAN>instead of
AsO<SUB>4</SUB><SUP>3-<SPAN class=Apple-converted-space> </SPAN></SUP>?
We also have other evidences including XANES and vibrational spectroscopy to
support this conclusion. However, using C2 as the initial model we obtained
samll sigma2 (~0.0007). This seems too small and out of the normal range
(0.002 每 0.03) as you mentioned in your publications (XAFS for everyone). So,
my question is if our data are reasonable. If yes, could you provid some
references to support?</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>By the way, I asked simialr question on the ifeffit forum
and you gave me some answer. However, the reviewer was not convinced and he
insited on that sigma2 must be in the range of 0.002-0.03. How can I response
this question?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=4>Any help is very appreciated.</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>Best regards,</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4>Shaofeng</FONT></DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV><FONT size=4></FONT> </DIV>
<DIV
style="FONT-FAMILY: century; FONT-SIZE: 14pt">--------------------------------------<BR>Shaofeng
Wang, Ph.D of Geochemistry<BR>Environmental Molecular Science
Group<BR>Institute of Applied Ecology, Chinese Academy of
Sciences<BR>Shenyang, 110016, China<BR><A
href="mailto:wangshaofeng@iae.ac.cn">wangshaofeng@iae.ac.cn</A><BR><A
href="http://www.iae.cas.cn/">www.iae.cas.cn</A><BR><BR></DIV></DIV></DIV></DIV></BLOCKQUOTE></DIV></DIV></DIV></DIV></DIV></BODY></HTML>