=head1 ARTEMIS: Automated First Shell Theory

B<ARTEMIS> - Automated first shell theory

Sometimes thinking about a fitting model is more than a problem
merits.  You just want a quick 'n' dirty stab at the first shell --
perhaps to measure the centroid of the distribution, perhaps to tell
if a sample is 4- or 6-coordinated.  Whatever.

B<Artemis> is not extremely well suited to rapid-fire, first shell
analysis.  By design, B<Artemis> tends to force the user to slow down
and think hard about every step.  B<Artemis> is powerful, but she
ain't simple.

The quick first shell (QFS) theory tool is an attempt at addressing
this shortcoming.  It works like this:

=over 4

=item 1.

Import some data.  Set the Fourier transform and fitting parameters to
suitable values.  Specifically, be sure to set the fitting range such
that it encloses the first peak of the data.

=item 2.

Select "Quick first shell theory" from the Theory menu.  This will
display the QFS dialog.

=item 3.

The QFS dialog provides spaces for selecting the parameters for a
simple first shell theory.  These include the atomic species of the
absorber and the scatterer, the absorption edge of the experiment, the
approximate distance between the absorber and scatterer, and the
coordination geometry to use in the B<Feff> calculation.

Currently the following coordination geomatries are available:

=over 4

=item *

4-coordinate crystal

=item *

6-coordinate crystal

=item *

octahedral molecule

=item *

tetrahedral molecule

=item *

square-planar molecule

=back

The QFS theory is probably not highly sensitive to the choice of
coordination geometry.  Since the unknown sample is probably not well
described by any of these geometries, they are all merely
approximations for use in a quick 'n' dirty fit.

=item 4.

Once you have set up the parameters for the QFS theory, click the "Do
it!" button.  This will step through the following without pausing:

=over 4

=item a.

Build an input file for the B<Feff> calculation

=item b.

Run B<Feff>

=item c.

Import the first path from the B<Feff> calculation

=item d.

Create a set of guess parameters for the amplitude, the sigma^2, the
e0, and the delta R.  Also created are set parameters for the third
and fourth cumulants, but they are set to zero.  These higher cumulant
set parameters are created to make it easy to consider higher
cumulants in subsequent fits merely by changing them from set to
guess.

=back


=back

If you have a mixed first shell, you might choose to repeat steps 2
through 4 two or more times.

At the end of this sequence, you are left with B<Artemis> in its
normal state.  You may need to adjust the parameters used in the fit.
The QFS dialog is really just a tool for initially setting up the
project.  It in no way changes the normal operation of B<Artemis>.

If you import data from an B<Athena> project file, the species of the
absorber and the edge will be set correctly when you start the dialog.


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=item

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