| 1 | <html> |
|---|
| 2 | <head> |
|---|
| 3 | <META NAME="Author" CONTENT="Brian H. Toby"> |
|---|
| 4 | <title>EXPGUI Tutorial #9</title> |
|---|
| 5 | </head> |
|---|
| 6 | <style> |
|---|
| 7 | A:link {text-decoration:none} |
|---|
| 8 | A:vlink {text-decoration:none} |
|---|
| 9 | </style> |
|---|
| 10 | |
|---|
| 11 | <BODY BGCOLOR="#FFFFFF" |
|---|
| 12 | topmargin="0" leftmargin="0" marginwidth="0" marginheight="0" |
|---|
| 13 | text="#000000" link="#0033ff" vlink="#0033ff" alink="#0033ff"> |
|---|
| 14 | |
|---|
| 15 | <? |
|---|
| 16 | include("/var/www/include/navigation.inc"); |
|---|
| 17 | include("/var/www/include/utility.inc"); |
|---|
| 18 | ?> |
|---|
| 19 | <blockquote> |
|---|
| 20 | |
|---|
| 21 | <CENTER> |
|---|
| 22 | <H1>GSAS Nickel example using EXPGUI (part 9)</H1> |
|---|
| 23 | </CENTER> |
|---|
| 24 | <H1> |
|---|
| 25 | 9. Additional Work |
|---|
| 26 | </H1> |
|---|
| 27 | This page describes other crystallographic and experimental |
|---|
| 28 | parameters that one would very likely need to refine to obtain |
|---|
| 29 | a reasonable model. |
|---|
| 30 | |
|---|
| 31 | <H2>Cell</H2> |
|---|
| 32 | <UL> |
|---|
| 33 | The fit obtained in the first refinement cycle is unusually good, because |
|---|
| 34 | in most cases the starting cell dimensions are only approximate. To |
|---|
| 35 | include the cell dimensions in the refinement, click on the |
|---|
| 36 | "Refine Cell" checkbutton on the Phase pane (see below). |
|---|
| 37 | <BR> |
|---|
| 38 | <img src="refcell.gif"> |
|---|
| 39 | <BR> |
|---|
| 40 | At this point it is wise to run GENLES again before adding additional |
|---|
| 41 | parameters to the refinement and to then run POWPREF before any |
|---|
| 42 | additional refinements. |
|---|
| 43 | </UL> |
|---|
| 44 | |
|---|
| 45 | <P><H2>Zero</H2> |
|---|
| 46 | <UL> |
|---|
| 47 | Another variable that should be included in a refinement for every |
|---|
| 48 | histogram is the zero offset. (The one exception is for lab x-ray |
|---|
| 49 | data, where the "shft" profile term should be refined instead.) |
|---|
| 50 | This is done on the Histogram pane, by selecting each |
|---|
| 51 | histogram and pressing the "Refine zero" button. |
|---|
| 52 | <BR> |
|---|
| 53 | <img src="global.gif" align=left> |
|---|
| 54 | It is also possible to set the zero flag for multiple histograms. Use the |
|---|
| 55 | "multiple histogram selection" option to group TOF histograms. Then |
|---|
| 56 | select all histograms by dragging both histograms (or using a right-mouse |
|---|
| 57 | click). The zero button the affects all selected histograms. |
|---|
| 58 | <BR clear=left> |
|---|
| 59 | <img src="refcell.gif"> |
|---|
| 60 | |
|---|
| 61 | </UL> |
|---|
| 62 | <BR clear=left> |
|---|
| 63 | <P><H2>Background Coefficients</H2> |
|---|
| 64 | <UL> |
|---|
| 65 | <img src="bkgterms.gif" align=left> |
|---|
| 66 | The GSAS tutorial in the manual recommends adding more background coefficients |
|---|
| 67 | to the first histogram, to allow more flexibility in the fit. This can be done |
|---|
| 68 | in EXPGUI from the Histogram pane, by first selecting the |
|---|
| 69 | histogram to be modified and then by pressing the the |
|---|
| 70 | "Edit Background" button. (If you are in multiple histogram selection mode, |
|---|
| 71 | as described above, the button is labeled "Globally Edit Background" -- but be |
|---|
| 72 | sure in this case to only edit the histogram(s) you want to change). |
|---|
| 73 | Change the number of terms by selecting the appropriate value, when |
|---|
| 74 | you click on the "Number of terms" button. Note that leaving a field |
|---|
| 75 | blank (as is seen for terms 5 & 6) is equivalent to setting them to zero. |
|---|
| 76 | Press "Set" to complete making this change. |
|---|
| 77 | |
|---|
| 78 | </UL> |
|---|
| 79 | <BR clear=left> |
|---|
| 80 | <P><H2>Atom Parameters</H2> |
|---|
| 81 | <UL> |
|---|
| 82 | The GSAS tutorial in the manual also recommends refining the atomic |
|---|
| 83 | displacement parameter (aka temperature factor) for the Ni atom to obtain |
|---|
| 84 | a better fit. This is done on the phase pane by selecting the Ni atom in |
|---|
| 85 | the middle box. This causes the atom parameters to be loaded at the bottom. |
|---|
| 86 | These values could be edited, but the only thing that needs to be done |
|---|
| 87 | in this case is to press the "U" refinement flag checkbutton. |
|---|
| 88 | <img src="refu.gif"> |
|---|
| 89 | |
|---|
| 90 | </UL> |
|---|
| 91 | <P><H2>Other Parameters</H2> |
|---|
| 92 | <UL> |
|---|
| 93 | The GSAS tutorial in the manual recommends |
|---|
| 94 | refining the absorption coefficient and perhaps the extinction parameter. |
|---|
| 95 | This cannot be done from EXPGUI, but it is simple to press the EXPEDT button |
|---|
| 96 | or menu item. This will cause any current changes to the .EXP file to be |
|---|
| 97 | saved and EXPEDT will be run in a separate window. |
|---|
| 98 | </UL> |
|---|
| 99 | |
|---|
| 100 | <BR clear=left><HR> |
|---|
| 101 | Previous step: <A HREF="nickel8.html"> |
|---|
| 102 | Run GENLES</A> |
|---|
| 103 | <BR> |
|---|
| 104 | Top: <A HREF="index.html"> |
|---|
| 105 | Introduction</A> |
|---|
| 106 | <BR> |
|---|
| 107 | |
|---|
| 108 | <HR> |
|---|
| 109 | </blockquote> |
|---|
| 110 | <P><font size=-1><A HREF="MAILTO:crystal@NIST.gov?subject=WWW page <?=$PHP_SELF?>">Comments, corrections or questions: crystal@NIST.gov</A></font><BR> |
|---|
| 111 | <font size=-1><? lastmod(); ?> </font> |
|---|
| 112 | <BR>$Revision: 591 $ $Date: 2009-12-04 23:08:44 +0000 (Fri, 04 Dec 2009) $ |
|---|
| 113 | </body> |
|---|
| 114 | </html> |
|---|
