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GSAS Nickel example using EXPGUI (part 7)

7. Setup for Least-Squares Refinement

Before the model can be refined to better fit the data, the structure must be entered. When starting with a new model it is a good idea to refine the scale factors for each histogram and the background terms before refining any structural parameters. So EXPGUI will be used to check which parameters are set to be refined. add new atom Select a phase by pressing the "1" button in the upper left. Then add an atom to the model by pressing the "Add New Atom" button in the lower right side of the Phase pane (shown in part 2). After entering the atom type, the coordinates added, and changing the Uiso value to match the example, press "Add" to add the atom to the .EXP file.

add atom result A box then appears, as shown to the left, to show the results when the atom is read into EXPTOOL.

atom phase page
Note that the atom now appears on the phase page. Also note that the cell will not be refined, since the "Refine Cell" checkbutton in the upper right is not checked. Nor are any atomic parameters being refined, since X V and F do not appear in the ref./damp column.

refine cell
We then check each histogram from the Histogram pane, and see that the background function has been set to type 4, with 4 terms, as recommended in the tutorial, and that no diffractometer constants will be refined (above and below).
type 4

unrefined constants
We can quickly confirm that the scale factors for the two histograms will be refined on the Scaling pane (above and below).
scaling pane

scaling pane 2
Finally we check that no profile terms are being refined on the Profile panes. (above and below).
profile panes

(.EXP Snapshot: nickel7.exp )

Previous step: Plot data using POWPLOT or LIVEPLOT
Next step: Run GENLES

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Last modified 02-August-2007 by website owner: NCNR (attn: Craig Brown)
$Revision: 1.4 $ $Date: 2002/04/12 21:21:18 $