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<p class="MsoNormal"><span style="color:#1F497D">Dear all<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">A few months ago I emailed about a problem that I have been having trying to use GSAS-II. The problem is that the structure which I am trying to refine is a silicate framework structure, there are four restraints
for each tetrahedrally coordinated site but for some reason GSAS-II doesn’t include all of them (see below).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">So I used the old GSAS instead I have got a reasonable fit, with all my tetrahedrally coordinated site restraints in place. However, the 3 strongest peaks are not well fitted, there is clearly something not quite
right with the peak shape, something is wrong with asymmetry of the peak shape.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I am using profile function 3 in the old GSAS, this uses S/L and H/L to define the asymmetry. I determined these from a Rietveld refinement of a silicon standard and then I have kept these silicon S/L and H/L
terms fixed in the refinement of my silicate framework structure.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">My problem is that my structure is low symmetry (P21/c monoclinic, with a b c all about 13 angstroms, beta about 93 degrees. My I11 data from the postal service has a wavelength of 0.8259 angstroms. Peak overlap
is a big problem with such a short wavelength, which is the only wavelength that diamond can offer for their postal service. I am finding that I am getting a much better fit with my PANalytical X’Pert machine with Cu K-alpha than with one of the best synchrotron
powder beamlines in the world!<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Has anyone got any advice on how to better model the peak shape in the old GSAS, or how to get all of my restraints included into the new GSAS?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">I am sure I could publish the structure from the X’Pert data, but as an old synchrotron scientist it would be good to include the synchrotron data in my paper.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Best wishes<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Dr. Tony Bell<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Senior X-ray Technician<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Materials and Research Engineering Institute<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Sheffield Hallam University<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN" style="color:#1F497D">City Campus<br>
Howard Street<br>
Sheffield<br>
S1 1WB<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN" style="color:#1F497D"><a href="mailto:Anthony.Bell@shu.ac.uk"><span style="color:blue">Anthony.Bell@shu.ac.uk</span></a><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN" style="color:#1F497D">0114 </span><span style="color:#1F497D">225 3401<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> gsas-ii-bounces@aps.anl.gov [mailto:gsas-ii-bounces@aps.anl.gov]
<b>On Behalf Of </b>Bell, Anthony<br>
<b>Sent:</b> 18 July 2016 15:49<br>
<b>To:</b> 'gsas-ii@mailman.aps.anl.gov'<br>
<b>Subject:</b> [GSAS-II] GSAS-II questions<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dear all<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks to the replies to my emails last week. I am still struggling up the learning curve with GSAS-II.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have done two of the tutorials with GSAS-II so I am now returning to some of my own data, recently collected for me on I11 at diamond light source. I had done a reasonable refinement using laboratory XRD data here in Sheffield, I am now
trying this refinement with synchrotron data to get a better refined crystal structure. My FULLPROF refinement of these data was reasonably good but not great, as I wasn’t sure of some of the peak width terms to use for I11. I knew with GSAS I could include
an instrument parameter file which would hopefully give me a better starting model for the peak width terms.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Two questions.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is it possible to refine some peak asymmetry terms in the peak width parameters in GSAS-II?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">My synchrotron data is on a synthetic mineral sample with tetrahedrally coordinated silicate framework structure. I wish to put in Si-O bond restraints. I know that there should be 4 Si-O bonds per tetrahedrally coordinates silicon, each
bond should be about 1.61 angstroms in length. However, when I add restraints not all of the silicon atoms have 4 Si-O bond restraints calculated, some only have 3 or 2 Si-O bond restraints? Is there some way of manually adding restraints? My previous FULLPROF
refinement had 4 Si-O bond length restraints per Si, is it possible to import restraints from a FULLPROF input file?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks in advance<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Dr. Tony Bell<o:p></o:p></p>
<p class="MsoNormal">Senior X-ray Technician<o:p></o:p></p>
<p class="MsoNormal">Materials and Research Engineering Institute<o:p></o:p></p>
<p class="MsoNormal">Sheffield Hallam University<o:p></o:p></p>
<p class="MsoNormal"><span lang="EN">City Campus<br>
Howard Street<br>
Sheffield<br>
S1 1WB<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN"><o:p> </o:p></span></p>
<p class="MsoNormal"><a href="mailto:Anthony.Bell@shu.ac.uk"><span lang="EN">Anthony.Bell@shu.ac.uk</span></a><span lang="EN"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN">0114 </span>225 3401<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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