[Ifeffit] mxan and gnxas

Francesco Giannici zenarcade at libero.it
Sat Jul 29 13:19:18 CDT 2006

1. how to get mxan: as far as i know, mxan is available free of charge, although not ready for download. you should directly contact maurizio dot benfatto @ lnf dot infn dot it. caveat: the documentation is *very* short, and there is no interface, so here's another reason to keep in touch with the developer.
mxan means "minuit xanes", so it uses the minuit minimization procedures to fit either structural (i.e. atomic positions) or physical (i.e. broadening, plasmon, etc.) parameters. it seems the best choice if you deal with a few atoms (biomolecules, coordination compounds, and such).

2. my two cents on gnxas: this package is either very powerful, and very scary. you have to be always aware of what you're doing, because it's no black box. but once you manage to learn the basics, you are awarded with wonderful quality and stability of the fit (minuit is used to avoid false minima during minimization), and total control of the background subtraction (spline and multi-electron excitation refined simultaneously during the fit). other useful features are asymmetric distributions, and the automatic inclusion of all ms paths in the n-body signal generation. the cons: there's no fourier filtering (the fit is done on chi(E)), there are a few bugs in the potential calculation that prevent a smooth generation of signals above 7 angstrom, and you have to spend a lot of time learning the various modules of the package.

hope this can help,
francesco giannici
dept. of inorganic and analytical chemistry
università di palermo
giannici at pa.ismn.cnr.it

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