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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span style='color:#1F497D'>Dear Dr. Tucker,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Sorry for the late reply, I was applying for graduate positions which consumed most of my time. As for my system, the nanoparticles are spherical with a diameter of 3.5 nm and a composition of Ni<sub>30</sub>Pd<sub>70</sub>. I think with a nanoparticle this small I should be able to simulate the whole particle, right? Since the structure is loosely FCC I would like to use a maximal coordination constraint, for this system a coordination of 12. Can this be done in RMCProfile, and if so how? Also, what is the formula for the conversion of the neutron weights to x-ray weights?<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Thank you very much and Happy New Year,<o:p></o:p></span></p><p class=MsoNormal><span style='color:#1F497D'>Chris Wright<o:p></o:p></span></p><div><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b>From:</b> matt.tucker@stfc.ac.uk [mailto:matt.tucker@stfc.ac.uk] <br><b>Sent:</b> Friday, December 6, 2013 10:40 AM<br><b>To:</b> rmcprofile-users@rmcprofile.org<br><b>Cc:</b> christopher_wright@brown.edu<br><b>Subject:</b> RE: [RMCProfile-users] X-ray PDF use<o:p></o:p></p></div></div><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'>Dear Christopher,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo2'><![if !supportLists]><span lang=EN-GB style='color:#1F497D'><span style='mso-list:Ignore'>1)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-GB style='color:#1F497D'>Can RMCProfile fit x-ray PDF?: Yes<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'>What Chris Kerr says is not strictly true. RMCProfile can fit x-ray PDF data. <o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'>The x-ray F(Q) can be fitted with the XRAY_RECIPROCAL_DATA keyword. However, the x-ray form factors have to be in the data file and it has to be convolved with the simulation box size. There is a program call xray_to_rmc that will do this for you if supplied the data in the usual rmc format.<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'>For the x-ray PDF, since the q-dependant part has been divided out you can treat this as a neutron PDF with different weights. These weightings are defined using the keyword NEUTRON_COEFFICIENTS (sorry a bit confusing I know).<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'>We are writing a tutorial example to show how all this works and it will be in the minor update 6.5.2. This will be out in the next few weeks.<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'>As Chris Kerr says there are plans to fit the x-ray PDF in a more rigorous way. Once this is implemented it will be useful for all x-ray PDF data, as it will make a fairer comparison regardless of the atomic radii<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph style='text-indent:-.25in;mso-list:l0 level1 lfo2'><![if !supportLists]><span lang=EN-GB style='color:#1F497D'><span style='mso-list:Ignore'>2)<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-GB style='color:#1F497D'>How do you fit nanoparticles with RMCProfile?<o:p></o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoListParagraph><span lang=EN-GB style='color:#1F497D'>Sadly this is not an easy question to answer, there are three possible approaches. <o:p></o:p></span></p><p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo2'><![if !supportLists]><span lang=EN-GB style='color:#1F497D'><span style='mso-list:Ignore'>a.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-GB style='color:#1F497D'>The first is to treat the data as a bulk sample if the particle is large. If not then a modification function for the particle size could be applied but this isn’t implemented at present.<o:p></o:p></span></p><p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo2'><![if !supportLists]><span lang=EN-GB style='color:#1F497D'><span style='mso-list:Ignore'>b.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-GB style='color:#1F497D'>The second (as Chris says) is to put one particle in a large box and only fit out to a distance where it does not see its periodic repeat (RMC uses periodic boundary conditions). <o:p></o:p></span></p><p class=MsoListParagraph style='margin-left:1.0in;text-indent:-.25in;mso-list:l0 level2 lfo2'><![if !supportLists]><span lang=EN-GB style='color:#1F497D'><span style='mso-list:Ignore'>c.<span style='font:7.0pt "Times New Roman"'> </span></span></span><![endif]><span lang=EN-GB style='color:#1F497D'>Finally if you can build a starting configuration with particles in a matrix that is not too large (> ~40,000 atoms), then you can use the various constraints/restraints to hold things together and model it as normal. This of course is not trivial but probably the ideal solution. <o:p></o:p></span></p><p class=MsoNormal style='margin-left:.75in'><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal style='margin-left:.75in'><span lang=EN-GB style='color:#1F497D'>If you tell us some more about your system we can advise what your best approach is most likely to be.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'>Best wishes,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'>Matt<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'>. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-GB style='color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> <a href="mailto:rmcprofile-users-bounces@rmcprofile.org">rmcprofile-users-bounces@rmcprofile.org</a> [<a href="mailto:rmcprofile-users-bounces@rmcprofile.org">mailto:rmcprofile-users-bounces@rmcprofile.org</a>] <b>On Behalf Of </b>Christopher J. Wright<br><b>Sent:</b> 02 December 2013 00:36<br><b>To:</b> <a href="mailto:rmcprofile-users@rmcprofile.org">rmcprofile-users@rmcprofile.org</a><br><b>Subject:</b> [RMCProfile-users] X-ray PDF use<o:p></o:p></span></p></div></div><p class=MsoNormal><span lang=EN-GB><o:p> </o:p></span></p><p class=MsoNormal>Hi,<o:p></o:p></p><p class=MsoNormal>I am working with PDF data collected from an x-ray synchrotron source. The samples are nanoparticles of various size and compositions. Is it possible to model these particles using RMCprofile?<o:p></o:p></p><p class=MsoNormal>Thank you very much,<o:p></o:p></p><p class=MsoNormal>Christopher J. Wright<o:p></o:p></p><p class=MsoNormal>Brown University Chemistry Department<o:p></o:p></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p><p><span lang=EN-GB>-- <br>Scanned by iCritical. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-GB style='font-size:12.0pt;font-family:"Times New Roman","serif"'><o:p> </o:p></span></p></div></body></html>