fitting...

[Patrick Allen <allen42@llnl.gov>]

Bruce,

I have been playing around with Tkatoms, Athena, and Artemis
on the MAC OSX and things run fine.  I think I mentioned this recently,
and figured out some of my problems.  These are nice packages!

OK, now for the question to open a can of worms:
I tried fitting with FEFFIT vs other packages a few years ago and
found some differences in amplitude output between FEFFIT and
the 2 other packages (EXAFSPAK and RSXAP).  At the time,
I talked with Matt, Graham George, Corwin Booth,
and it was sort of left up in the air.

Now I have started comparing fitting with Artemis and EXAFSPAK and
noticed some differences again, so I decided to do a very simple test.
When I create a single EXAFS wave with FEFF8 and use this exact wave
to refit the data, I get the exact correct answer with EXAFSPAK.
With artemis in R-space or K-space fitting mode, I can't get the same
nice fit.  The problem looks like it's in the phase shift.
I'm not sure  what's going on, but my discussion last time ended by
looking at the 4psigma2/Reff term in FEFFIT's Chi(k) expression.

I would be curious to see what you think.

Thanks,

Pat

--

_______________________________________________
Dr. Patrick G. Allen, Deputy Director
Seaborg Institute for Transactinium Science
Lawrence Livermore National Laboratory
P.O. Box 808  MS L-231
Livermore CA 94551

phone:	925.423.8955
fax:	925.422.3160
email:  allen42@llnl.gov
________________________________________________