source: trunk/tutorial2/garnet6.html @ 465

Last change on this file since 465 was 173, checked in by toby, 12 years ago

# on 2000/05/30 22:22:38, toby did:
Garnet tutorial

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1<html>
2<head>
3   <META NAME="Author" CONTENT="Brian H. Toby">
4   <title>EXPGUI Tutorial #6</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>EXPGUI Tutorial: Garnet (part 6)</H1>
25</CENTER>
26<H1>
276. Additional Least-Squares Refinement
28</H1>
29The initial fit obtained in the previous runs is not particularly good. The
30<A HREF="garnet5.html#diff">"first derivative"</A>
31appearance in the difference plot peaks indicates that
32peaks are not correctly positioned, so refining the lattice parameters and
33zero point correction are the first order of business.
34<BR clear=left><P>
35<img src="fit1.gif">
36<BR clear=left>
37While normally I would recommend refining the lattice first and then
38in a subsequent refinement cycle also refining the zero point correction
39in a later cycle of refinement, with a cubic cell and a small
40zero-point error it is possible to refine both together. Set the refinement
41flag for the lattice (shown above) and the zero point correction (shown below).
42<BR clear=left><P>
43<img src="fit2.gif">
44<BR clear=left><P>
45and then start GENLES, as was done before.
46<BR clear=left><P>
47<img src="fit3.gif">
48<BR clear=left>
49A dramatic improvement is seen both through the agreement factors (above)
50and as seen in the plot (below).
51<BR clear=left><P>
52<a name="ticks"><img src="fit4.gif"></a>
53<BR clear=left><P>
54At this point it is a good idea to run POWPREF and GENLES again,
55since peak positions have moved. This causes the Reduced Chi**2 to drop from
5614.9 to 13.5.
57
58<P><BR>(.EXP Snapshot:
59<A HREF="ftp://ftp.ncnr.nist.gov/pub/cryst/gsas/tutorials/garnet6.exp">
60garnet6.exp
61</A>)
62
63<BR clear=left><HR>
64Previous step: <A HREF="garnet5.html">
65Plot data using POWPLOT or LIVEPLOT</A>
66</A>
67<BR>
68Next step: <A HREF="garnet7.html">
69Define Constraints</A>
70
71<BR clear=left>
72<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>)
73<BR clear=left>
74$Revision: 173 $ $Date: 2009-12-04 23:01:37 +0000 (Fri, 04 Dec 2009) $
75</body>
76</html>
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