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| 3 | <META NAME="Author" CONTENT="Brian H. Toby"> |
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| 4 | <title>EXPGUI Tutorial #9</title> |
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| 5 | </head> |
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[591] | 11 | <BODY BGCOLOR="#FFFFFF" |
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[591] | 15 | <? |
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| 16 | include("/var/www/include/navigation.inc"); |
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| 17 | include("/var/www/include/utility.inc"); |
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| 18 | ?> |
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| 19 | <blockquote> |
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| 20 | |
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[165] | 21 | <CENTER> |
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| 22 | <H1>GSAS Nickel example using EXPGUI (part 9)</H1> |
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| 23 | </CENTER> |
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| 24 | <H1> |
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| 25 | 9. Additional Work |
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| 26 | </H1> |
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| 27 | This page describes other crystallographic and experimental |
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| 28 | parameters that one would very likely need to refine to obtain |
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| 29 | a reasonable model. |
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| 30 | |
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| 31 | <H2>Cell</H2> |
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| 32 | <UL> |
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| 33 | The fit obtained in the first refinement cycle is unusually good, because |
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| 34 | in most cases the starting cell dimensions are only approximate. To |
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| 35 | include the cell dimensions in the refinement, click on the |
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| 36 | "Refine Cell" checkbutton on the Phase pane (see below). |
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| 37 | <BR> |
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| 38 | <img src="refcell.gif"> |
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| 39 | <BR> |
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| 40 | At this point it is wise to run GENLES again before adding additional |
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| 41 | parameters to the refinement and to then run POWPREF before any |
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| 42 | additional refinements. |
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| 43 | </UL> |
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| 44 | |
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| 45 | <P><H2>Zero</H2> |
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| 46 | <UL> |
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[212] | 47 | Another variable that should be included in a refinement for every |
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[165] | 48 | histogram is the zero offset. (The one exception is for lab x-ray |
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| 49 | data, where the "shft" profile term should be refined instead.) |
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| 50 | This is done on the Histogram pane, by selecting each |
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| 51 | histogram and pressing the "Refine zero" button. |
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| 52 | <BR> |
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| 53 | <img src="global.gif" align=left> |
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| 54 | It is also possible to set the zero flag for multiple histograms. Use the |
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| 55 | "multiple histogram selection" option to group TOF histograms. Then |
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| 56 | select all histograms by dragging both histograms (or using a right-mouse |
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| 57 | click). The zero button the affects all selected histograms. |
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| 58 | <BR clear=left> |
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| 59 | <img src="refcell.gif"> |
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| 60 | |
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| 61 | </UL> |
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| 62 | <BR clear=left> |
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| 63 | <P><H2>Background Coefficients</H2> |
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| 64 | <UL> |
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| 65 | <img src="bkgterms.gif" align=left> |
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| 66 | The GSAS tutorial in the manual recommends adding more background coefficients |
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| 67 | to the first histogram, to allow more flexibility in the fit. This can be done |
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[212] | 68 | in EXPGUI from the Histogram pane, by first selecting the |
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| 69 | histogram to be modified and then by pressing the the |
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| 70 | "Edit Background" button. (If you are in multiple histogram selection mode, |
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| 71 | as described above, the button is labeled "Globally Edit Background" -- but be |
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[165] | 72 | sure in this case to only edit the histogram(s) you want to change). |
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| 73 | Change the number of terms by selecting the appropriate value, when |
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| 74 | you click on the "Number of terms" button. Note that leaving a field |
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| 75 | blank (as is seen for terms 5 & 6) is equivalent to setting them to zero. |
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| 76 | Press "Set" to complete making this change. |
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| 77 | |
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| 78 | </UL> |
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| 79 | <BR clear=left> |
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| 80 | <P><H2>Atom Parameters</H2> |
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| 81 | <UL> |
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| 82 | The GSAS tutorial in the manual also recommends refining the atomic |
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| 83 | displacement parameter (aka temperature factor) for the Ni atom to obtain |
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| 84 | a better fit. This is done on the phase pane by selecting the Ni atom in |
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| 85 | the middle box. This causes the atom parameters to be loaded at the bottom. |
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| 86 | These values could be edited, but the only thing that needs to be done |
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| 87 | in this case is to press the "U" refinement flag checkbutton. |
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| 88 | <img src="refu.gif"> |
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| 89 | |
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| 90 | </UL> |
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| 91 | <P><H2>Other Parameters</H2> |
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| 92 | <UL> |
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| 93 | The GSAS tutorial in the manual recommends |
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| 94 | refining the absorption coefficient and perhaps the extinction parameter. |
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| 95 | This cannot be done from EXPGUI, but it is simple to press the EXPEDT button |
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| 96 | or menu item. This will cause any current changes to the .EXP file to be |
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| 97 | saved and EXPEDT will be run in a separate window. |
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| 98 | </UL> |
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| 99 | |
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| 100 | <BR clear=left><HR> |
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| 101 | Previous step: <A HREF="nickel8.html"> |
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| 102 | Run GENLES</A> |
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| 103 | <BR> |
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| 104 | Top: <A HREF="index.html"> |
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| 105 | Introduction</A> |
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| 106 | <BR> |
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| 107 | |
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[591] | 108 | <HR> |
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| 109 | </blockquote> |
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| 110 | <P><font size=-1><A HREF="MAILTO:crystal@NIST.gov?subject=WWW page <?=$PHP_SELF?>">Comments, corrections or questions: crystal@NIST.gov</A></font><BR> |
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| 111 | <font size=-1><? lastmod(); ?> </font> |
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| 112 | <BR>$Revision: 591 $ $Date: 2009-12-04 23:08:44 +0000 (Fri, 04 Dec 2009) $ |
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[165] | 113 | </body> |
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| 114 | </html> |
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