AUTOFIT 1 2, UPDATED SOFTWARE FOR XAS GLOBAL MAPPING

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Our global mapping procedure, where crystal structure coordinates are refined to XAS data using the ab initio XAS code FEFF 6.01, continues to be used and updated. In the programs, a grid of hundreds of simulations are directly compared to the experimental data without the use of non-linear least squares fitting procedures to find the interatomic distances. Instead, each simulation is performed with different interatomic distances. The emphasis is on mapping the local Hand global minima and providing a detailed visual picture and error Hanalysis in the comparison of alternative structures. The three Hdimensional structural coordinates utilized in the simulations are Hbased on crystal structure models derived from structural databases. HThus, a particular geometry for the metal site is incorporated in this Hchoice. Alternative structures with different geometries can also be Hselected, processed, and compared. This makes the structural Hassumptions about the site explicit and they must be justified based Hon ancillary structural information. Our suite of programs (called HAUTOFIT 1.2) vary selected bond distances, compare the resulting ab Hinitio simulations to the experimental data, and compute and plot a Hfigure that displays 400-500 alternative solutions simultaneously. HThese programs are available to outside users free of charge and have Hbeen readied for release along with a manual for using the code. In Haddition, we have recently completed a UNIX based version of the code, Halong with the original PC based version.