| 1 | <html> |
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| 2 | <head> |
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| 3 | <META NAME="Author" CONTENT="Brian H. Toby"> |
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| 4 | <title>EXPGUI Tutorial #4</title> |
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| 5 | </head> |
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| 6 | <BODY BGCOLOR="#FFFFFF"> |
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| 7 | |
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| 8 | <A HREF=http://www.ncnr.nist.gov> |
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| 9 | <IMG SRC="http://www.ncnr.nist.gov/images/ncnrtrans.gif" |
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| 10 | alt="Link to NIST Center for Neutron Research home page" |
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| 11 | ALIGN=RIGHT></A> |
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| 12 | <A HREF=http://www.nist.gov> |
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| 14 | alt="Link to National Institute of Standards & Technology home page" |
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| 15 | ALIGN=LEFT></A> |
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| 16 | <CENTER> |
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| 17 | <A Href="http://www.ncnr.nist.gov/programs/crystallography/software/tclpkgs.html"> |
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| 18 | <IMG SRC="tcltklogo100.gif" |
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| 19 | alt="Link to Tcl/Tk information"> |
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| 20 | </CENTER></A> |
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| 21 | <hr> |
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| 22 | |
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| 23 | <CENTER> |
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| 24 | <H1>EXPGUI Tutorial: Garnet (part 4)</H1> |
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| 25 | </CENTER> |
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| 26 | <H1> |
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| 27 | 4. Run POWPREF and GENLES |
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| 28 | </H1> |
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| 29 | <H3>POWPREF</H3> |
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| 30 | <img src="powpref2.gif" align=left> |
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| 31 | Before a least-squares refinement can be run, the POWPREF program |
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| 32 | must be run. This program assigns the reflections that are associated with |
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| 33 | each data point in each histogram. For this reason, POWPREF should |
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| 34 | be rerun if the lattice constants change, if peak widths or |
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| 35 | asymmetry parameters change or if you change the range of data |
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| 36 | that you are using in any histogram. |
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| 37 | <P> |
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| 38 | POWPREF can be run in one of three ways. It can be invoked from the |
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| 39 | menu item in the Powder menu (see to the left), or as a button in |
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| 40 | the button bar (see below) or by pressing the Alt-P key combination. |
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| 41 | <BR clear=left><P> |
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| 42 | <img src="powpref1a.gif"> |
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| 43 | <BR> |
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| 44 | <P> |
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| 45 | <img src="powpref3a.gif"> |
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| 46 | <BR> |
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| 47 | <img src="powpref4a.gif" align=left> |
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| 48 | Once POWPREF is started, a window is opened to watch the program |
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| 49 | progress, as is shown above. |
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| 50 | <P> |
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| 51 | Since POWPREF modifies the .EXP file, |
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| 52 | a message, as shown to the left, is displayed. |
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| 53 | Pressing "Load new" causes the new .EXP file to be reread. |
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| 54 | Pressing "Continue editing" causes EXPGUI to continue to edit the |
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| 55 | previous version of the .EXP file. If more changes are made, and |
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| 56 | the .EXP file is saved, the changes made by POWPREF will be lost. |
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| 57 | POWPREF makes only minor changes to the .EXP file, so there |
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| 58 | is little reason to reject the changes, but if a program, such |
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| 59 | as GENLES has made many incorrect changes to an experiment, the |
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| 60 | "Continue editing" option provides an easy way to keep the .EXP file |
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| 61 | from before the run. |
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| 62 | <BR clear=left> |
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| 63 | <P> |
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| 64 | <H3>GENLES</H3> |
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| 65 | At this point it is possible to run GENLES, to fit the initial background |
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| 66 | (three terms) and the scale factor (1 term). |
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| 67 | Similar to how POWPREF was invoked above, |
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| 68 | GENLES can be run from the appropriate |
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| 69 | button on the button bar, by typing Alt-G, or using the GENLES command |
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| 70 | in the Powder or Xtal menus. As soon as GENLES is started, a box appears |
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| 71 | on the screen showing the refinement status. (See below). |
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| 72 | |
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| 73 | <BR clear=left> |
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| 74 | <img src="genles2a.gif"> |
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| 75 | |
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| 76 | <BR> |
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| 77 | <img src="powpref4a.gif" align=left> |
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| 78 | When GENLES is finished and the window is |
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| 79 | closed, press "Load new" to cause the revised .EXP |
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| 80 | file to be read. (Pressing "Continue editing" would |
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| 81 | reject the results of the refinement.) |
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| 82 | |
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| 83 | <BR clear=left> |
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| 84 | <P><img src="lstview1.gif"> |
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| 85 | |
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| 86 | To examine the results of the refinement in more detail, |
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| 87 | consult the .LST file. This can be examined using the |
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| 88 | LSTVIEW program. This program is shown above. Note that the |
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| 89 | contents of the LSTVIEW box are updated as the refinement |
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| 90 | progresses. |
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| 91 | <P><BR>(.EXP Snapshot: |
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| 92 | <A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/garnet4.exp"> |
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| 93 | garnet4.exp |
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| 94 | </A>) |
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| 95 | |
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| 96 | <BR clear=left><HR> |
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| 97 | Previous step: <A HREF="garnet3.html"> |
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| 98 | Add data (histogram) to the Experiment |
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| 99 | </A> |
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| 100 | <BR> |
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| 101 | Next step: <A HREF="garnet5.html"> |
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| 102 | Plot data using POWPLOT or LIVEPLOT</A> |
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| 103 | |
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| 104 | <BR clear=left> |
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| 105 | <HR><p><a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>) |
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| 106 | <BR clear=left> |
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| 107 | $Revision: 171 $ $Date: 2009-12-04 23:01:35 +0000 (Fri, 04 Dec 2009) $ |
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| 108 | </body> |
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| 109 | </html> |
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