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1<html>
2<head>
3   <META NAME="Author" CONTENT="Brian H. Toby">
4   <title>EXPGUI Tutorial #9</title>
5</head>
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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>
259. Additional Work
26</H1>
27This page describes other crystallographic and experimental
28parameters that one would very likely need to refine to obtain
29a reasonable model.
30
31<H2>Cell</H2>
32<UL>
33The fit obtained in the first refinement cycle is unusually good, because
34in most cases the starting cell dimensions are only approximate. To
35include 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>
40At this point it is wise to run GENLES again before adding additional
41parameters to the refinement and to then run POWPREF before any
42additional refinements.
43</UL>
44
45<P><H2>Zero</H2>
46<UL>
47Another variable that should be included in a refinement for every
48histogram is the zero offset. (The one exception is for lab x-ray
49data, where the "shft" profile term should be refined instead.)
50This is done on the Histogram pane, by selecting each
51histogram and pressing the "Refine zero" button.
52<BR>
53<img src="global.gif" align=left>
54It is also possible to set the zero flag for multiple histograms. Use the
55"multiple histogram selection" option to group TOF histograms. Then
56select all histograms by dragging both histograms (or using a right-mouse
57click). 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>
66The GSAS tutorial in the manual recommends adding more background coefficients
67to the first histogram, to allow more flexibility in the fit. This can be done
68in EXPGUI from the Histogram pane, by first selecting the
69histogram to be modified and then by pressing the the
70"Edit Background" button. (If you are in multiple histogram selection mode,
71as described above, the button is labeled "Globally Edit Background" -- but be
72sure in this case to only edit the histogram(s) you want to change).
73Change the number of terms by selecting the appropriate value, when
74you click on the "Number of terms" button. Note that leaving a field
75blank (as is seen for terms 5 & 6) is equivalent to setting them to zero.
76Press "Set" to complete making this change.
77
78</UL>
79<BR clear=left>
80<P><H2>Atom Parameters</H2>
81<UL>
82The GSAS tutorial in the manual also recommends refining the atomic
83displacement parameter (aka temperature factor) for the Ni atom to obtain
84a better fit. This is done on the phase pane by selecting the Ni atom in
85the middle box. This causes the atom parameters to be loaded at the bottom.
86These values could be edited, but the only thing that needs to be done
87in 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>
93The GSAS tutorial in the manual recommends
94refining the absorption coefficient and perhaps the extinction parameter.
95This cannot be done from EXPGUI, but it is simple to press the EXPEDT button
96or menu item. This will cause any current changes to the .EXP file to be
97saved and EXPEDT will be run in a separate window.
98</UL>
99
100<BR clear=left><HR>
101Previous step: <A HREF="nickel8.html">
102Run GENLES</A>
103<BR>
104Top: <A HREF="index.html">
105Introduction</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: 930 $ $Date: 2009-12-04 23:14:35 +0000 (Fri, 04 Dec 2009) $
113</body>
114</html>
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