source: trunk/tutorial1/nickel9.html @ 495

Last change on this file since 495 was 212, checked in by toby, 12 years ago

# on 2000/06/09 03:57:42, toby did:
incorporate many useful comments by Egbert Keller

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  • Property rcs:date set to 2000/06/09 03:57:42
  • Property rcs:lines set to +6 -5
  • Property rcs:rev set to 1.2
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  • Property svn:keywords set to Author Date Revision Id
File size: 4.0 KB
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1<html>
2<head>
3   <META NAME="Author" CONTENT="Brian H. Toby">
4   <title>EXPGUI Tutorial #9</title>
5</head>
6<BODY BGCOLOR="#FFFFFF">
7
8<A HREF=http://www.ncnr.nist.gov>
9<IMG SRC="http://www.ncnr.nist.gov/images/ncnrtrans.gif" 
10alt="Link to NIST Center for Neutron Research home page"
11ALIGN=RIGHT></A>
12<A HREF=http://www.nist.gov>
13<IMG SRC="http://www.ncnr.nist.gov/images/webidblue_2lineright.gif" 
14alt="Link to National Institute of Standards & Technology home page"
15ALIGN=LEFT></A>
16<CENTER>
17<A Href="http://www.ncnr.nist.gov/programs/crystallography/software/tclpkgs.html">
18<IMG SRC="tcltklogo100.gif" 
19alt="Link to Tcl/Tk information">
20</CENTER></A>
21<hr>
22
23<CENTER>
24<H1>GSAS Nickel example using EXPGUI (part 9)</H1>
25</CENTER>
26<H1>
279. Additional Work
28</H1>
29This page describes other crystallographic and experimental
30parameters that one would very likely need to refine to obtain
31a reasonable model.
32
33<H2>Cell</H2>
34<UL>
35The fit obtained in the first refinement cycle is unusually good, because
36in most cases the starting cell dimensions are only approximate. To
37include the cell dimensions in the refinement, click on the
38"Refine Cell" checkbutton on the Phase pane (see below).
39<BR>
40<img src="refcell.gif">
41<BR>
42At this point it is wise to run GENLES again before adding additional
43parameters to the refinement and to then run POWPREF before any
44additional refinements.
45</UL>
46
47<P><H2>Zero</H2>
48<UL>
49Another variable that should be included in a refinement for every
50histogram is the zero offset. (The one exception is for lab x-ray
51data, where the "shft" profile term should be refined instead.)
52This is done on the Histogram pane, by selecting each
53histogram and pressing the "Refine zero" button.
54<BR>
55<img src="global.gif" align=left>
56It is also possible to set the zero flag for multiple histograms. Use the
57"multiple histogram selection" option to group TOF histograms. Then
58select all histograms by dragging both histograms (or using a right-mouse
59click). The zero button the affects all selected histograms.
60<BR clear=left>
61<img src="refcell.gif">
62
63</UL>
64<BR clear=left>
65<P><H2>Background Coefficients</H2>
66<UL>
67<img src="bkgterms.gif" align=left>
68The GSAS tutorial in the manual recommends adding more background coefficients
69to the first histogram, to allow more flexibility in the fit. This can be done
70in EXPGUI from the Histogram pane, by first selecting the
71histogram to be modified and then by pressing the the
72"Edit Background" button. (If you are in multiple histogram selection mode,
73as described above, the button is labeled "Globally Edit Background" -- but be
74sure in this case to only edit the histogram(s) you want to change).
75Change the number of terms by selecting the appropriate value, when
76you click on the "Number of terms" button. Note that leaving a field
77blank (as is seen for terms 5 & 6) is equivalent to setting them to zero.
78Press "Set" to complete making this change.
79
80</UL>
81<BR clear=left>
82<P><H2>Atom Parameters</H2>
83<UL>
84The GSAS tutorial in the manual also recommends refining the atomic
85displacement parameter (aka temperature factor) for the Ni atom to obtain
86a better fit. This is done on the phase pane by selecting the Ni atom in
87the middle box. This causes the atom parameters to be loaded at the bottom.
88These values could be edited, but the only thing that needs to be done
89in this case is to press the "U" refinement flag checkbutton.
90<img src="refu.gif">
91
92</UL>
93<P><H2>Other Parameters</H2>
94<UL>
95The GSAS tutorial in the manual recommends
96refining the absorption coefficient and perhaps the extinction parameter.
97This cannot be done from EXPGUI, but it is simple to press the EXPEDT button
98or menu item. This will cause any current changes to the .EXP file to be
99saved and EXPEDT will be run in a separate window.
100</UL>
101
102<BR clear=left><HR>
103Previous step: <A HREF="nickel8.html">
104Run GENLES</A>
105<BR>
106Top: <A HREF="index.html">
107Introduction</A>
108<BR>
109
110<BR clear=left>
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>)
112<BR clear=left>
113$Revision: 212 $ $Date: 2009-12-04 23:02:16 +0000 (Fri, 04 Dec 2009) $
114</body>
115</html>
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