| 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 #9</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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| 13 | <IMG SRC="http://www.ncnr.nist.gov/images/webidblue_2lineright.gif" |
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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>GSAS Nickel example using EXPGUI (part 9)</H1> |
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| 25 | </CENTER> |
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| 26 | <H1> |
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| 27 | 9. Additional Work |
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| 28 | </H1> |
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| 29 | This page describes other crystallographic and experimental |
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| 30 | parameters that one would very likely need to refine to obtain |
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| 31 | a reasonable model. |
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| 32 | |
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| 33 | <H2>Cell</H2> |
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| 34 | <UL> |
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| 35 | The fit obtained in the first refinement cycle is unusually good, because |
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| 36 | in most cases the starting cell dimensions are only approximate. To |
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| 37 | include the cell dimensions in the refinement, click on the |
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| 38 | "Refine Cell" checkbutton on the Phase pane (see below). |
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| 39 | <BR> |
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| 40 | <img src="refcell.gif"> |
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| 41 | <BR> |
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| 42 | At this point it is wise to run GENLES again before adding additional |
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| 43 | parameters to the refinement and to then run POWPREF before any |
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| 44 | additional refinements. |
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| 45 | </UL> |
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| 46 | |
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| 47 | <P><H2>Zero</H2> |
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| 48 | <UL> |
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| 49 | Another variable that should be included in a refinement for every |
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| 50 | histogram is the zero offset. (The one exception is for lab x-ray |
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| 51 | data, where the "shft" profile term should be refined instead.) |
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| 52 | This is done on the Histogram pane, by selecting each |
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| 53 | histogram and pressing the "Refine zero" button. |
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| 54 | <BR> |
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| 55 | <img src="global.gif" align=left> |
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| 56 | It is also possible to set the zero flag for multiple histograms. Use the |
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| 57 | "multiple histogram selection" option to group TOF histograms. Then |
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| 58 | select all histograms by dragging both histograms (or using a right-mouse |
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| 59 | click). The zero button the affects all selected histograms. |
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| 60 | <BR clear=left> |
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| 61 | <img src="refcell.gif"> |
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| 62 | |
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| 63 | </UL> |
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| 64 | <BR clear=left> |
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| 65 | <P><H2>Background Coefficients</H2> |
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| 66 | <UL> |
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| 67 | <img src="bkgterms.gif" align=left> |
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| 68 | The GSAS tutorial in the manual recommends adding more background coefficients |
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| 69 | to the first histogram, to allow more flexibility in the fit. This can be done |
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| 70 | in EXPGUI from the Histogram pane, by first selecting the |
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| 71 | histogram to be modified and then by pressing the the |
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| 72 | "Edit Background" button. (If you are in multiple histogram selection mode, |
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| 73 | as described above, the button is labeled "Globally Edit Background" -- but be |
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| 74 | sure in this case to only edit the histogram(s) you want to change). |
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| 75 | Change the number of terms by selecting the appropriate value, when |
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| 76 | you click on the "Number of terms" button. Note that leaving a field |
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| 77 | blank (as is seen for terms 5 & 6) is equivalent to setting them to zero. |
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| 78 | Press "Set" to complete making this change. |
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| 79 | |
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| 80 | </UL> |
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| 81 | <BR clear=left> |
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| 82 | <P><H2>Atom Parameters</H2> |
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| 83 | <UL> |
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| 84 | The GSAS tutorial in the manual also recommends refining the atomic |
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| 85 | displacement parameter (aka temperature factor) for the Ni atom to obtain |
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| 86 | a better fit. This is done on the phase pane by selecting the Ni atom in |
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| 87 | the middle box. This causes the atom parameters to be loaded at the bottom. |
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| 88 | These values could be edited, but the only thing that needs to be done |
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| 89 | in this case is to press the "U" refinement flag checkbutton. |
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| 90 | <img src="refu.gif"> |
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| 91 | |
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| 92 | </UL> |
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| 93 | <P><H2>Other Parameters</H2> |
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| 94 | <UL> |
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| 95 | The GSAS tutorial in the manual recommends |
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| 96 | refining the absorption coefficient and perhaps the extinction parameter. |
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| 97 | This cannot be done from EXPGUI, but it is simple to press the EXPEDT button |
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| 98 | or menu item. This will cause any current changes to the .EXP file to be |
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| 99 | saved and EXPEDT will be run in a separate window. |
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| 100 | </UL> |
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| 101 | |
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| 102 | <BR clear=left><HR> |
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| 103 | Previous step: <A HREF="nickel8.html"> |
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| 104 | Run GENLES</A> |
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| 105 | <BR> |
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| 106 | Top: <A HREF="index.html"> |
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| 107 | Introduction</A> |
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| 108 | <BR> |
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| 109 | |
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| 110 | <BR clear=left> |
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| 111 | <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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| 112 | <BR clear=left> |
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| 113 | $Revision: 212 $ $Date: 2009-12-04 23:02:16 +0000 (Fri, 04 Dec 2009) $ |
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| 114 | </body> |
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| 115 | </html> |
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