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<div class="moz-cite-prefix">Dear Brian,<br>
<br>
if I may to drop the comment. The enquiry is not entirely without
merit. It is not infrequent that one combines information from
many sources to build a model and constrains help to fix
deficiency of a single method. I guess that one case where a hard
limit could be useful is a case of vacancies in non-stoichiometric
compounds. As you say it is easy to constrain a site shared by
multiple elements if they add up to 1.� Yet, there has been always
a problem, also for GSAS I, to deal with a sum of vacancy +
element on a site. From this what I observed the refinement was
trying to compensate vacancies with artificiality increased
thermal displacement parameters if the data at higher 2-Theta were
not "perfect" (actually only a case of good TOF with neutrons or
an exceptional quality X-ray diffraction).� If I know that the
occupancy cannot be larger than e.g. 1 for a site from other
sources (e.g. spectroscopy or other x-ray neutron diffraction
experiments) then it should be possible to set a hard limit on the
site. Of course such decision must be well substantiated.
Otherwise one risks producing some rubbish results...<br>
<br>
Best wishes<br>
<br>
Andrzej<br>
<br>
<br>
<br>
Am 12.09.2016 um 11:42 schrieb Toby, Brian H.:<br>
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No.�
<div class=""><br class="">
</div>
<div class="">To be honest I am not sure why one would want to do
this. When a parameter refines "out of range� it tells you
something about your data or model. With a restraint, you would
never know that for example, a Uiso value is refining negative
by > 2 sigma or a occupancy is >>1. It makes sense to
me to define a model so that the sum of occupancies is fixed � a
well defined assumption. Defining a range for a parameter scares
me as I could never know that my model is highly flawed is some
way.�</div>
<div class=""><br class="">
</div>
<div class="">Brian<br class="">
<div class=""><br class="">
<div>
<blockquote type="cite" class="">
<div class="">On Sep 12, 2016, at 10:27 AM, Ivo Alxneit
<<a moz-do-not-send="true"
href="mailto:ivo.alxneit@psi.ch" class="">ivo.alxneit@psi.ch</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="">Dear all<br class="">
<br class="">
is there a way to restrict fitted parameters to a
certain range? For<br class="">
example restrict site occupancies to positive numbers
or to a range such<br class="">
as 0.9-1.0?<br class="">
<br class="">
thanks for any help<br class="">
-- <br class="">
Dr. Ivo Alxneit<br class="">
Catalysis for Energy Group<br class="">
Bioenergy and Catalysis Laboratory �������phone: +41
56 310 4092<br class="">
Paul Scherrer Institute ��������������������fax: +41
56 310 2688<br class="">
CH-5232 Villigen ���������������������gnupg key:
0x515E30C7<br class="">
Switzerland<br class="">
<a moz-do-not-send="true"
href="https://www.psi.ch/ceg/catalysis-for-energy-group/"
class="">https://www.psi.ch/ceg/catalysis-for-energy-group/</a><br
class="">
<br class="">
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<pre class="moz-signature" cols="72">--
--
Dr. Andrzej Falenty <a class="moz-txt-link-rfc2396E" href="mailto:afalent@uni-goettingen.de"><afalent@uni-goettingen.de></a>
Abt. Kristallographie
GZG, Georg-August-Universit�t
Goldschmidtstra�e 1
D-37077 G�ttingen
Tel. 0049 551 3912546
<a class="moz-txt-link-freetext" href="http://kristall.uni-mki.gwdg.de/">http://kristall.uni-mki.gwdg.de/</a></pre>
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