Kristine, This is a difficult thing to do. Assuming I read your question correctly. I believe that you are trying to calculate the XANES from a Mn2+, Mn3+, etc, ion. The only way that I have been able to get reasonable results is to accurately calculate the XANES with FEFF using a couterion in its correct position. This has led to some very large calculations on my part. The ION card in FEFF is not terribly effective which is too bad, but I understand the difficulty. I would almost suggest that it be removed. I have done many calculations for Mn compounds that I have been working on over the last couple of years and am pretty happy with the experimental/ theoretical agreement that I have been getting, lately. This may have been a better question for the feffusers mailing list. Jeff Terry IIT On Jan 22, 2004, at 3:28 PM, k-kupiecki@northwestern.edu wrote:

Hi ,

I'm trying to help a collegue who would like to use FEFF to simulate X-ray absorption spectra for a single ion (i.e. Mn+2, Mn+3, Mn+4...) through the Mn L3/L2 edge. Since this is quite different from using FEFF for EXAFS like I'm used to... I could really use some help in figuring out how to accomplish this.

We were also trying to figure out a way to remove the background from his experimental absorption spectra -- can Athena do this (or does Athena only work on EXAFS spectra)? If not, does anyone do this type of thing and have suggestions?

Thanks!!! Sincerely,

Kristine Witkowski Northwestern University

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Dear Kristine, FEFF is not set up to calculate single Mn ions. However, you could try to simulate this approximately by taking a Mn cluster, varying the Fermi energy (which adjusts the ionicity) and plotting only the atomic-like backgound mu_0 (col 5 in xmu.dat). Unfortunately, for Mn and other transition elements there are large "local field effects," i.e., screening of the x-ray field at the L_23 edge, which cause the L3/L2 ratio to vary. For this reason independent electron calculations are not likely to be reliable for such transition elements. For details, see e.g., ``Dynamic screening effects in x-ray absorption spectra," A.\ L. Ankudinov A.\ I. Nesvizhskii, and J. J. Rehr, Phys. Rev. B. {\bf67}, 115120 (2003). Also the absorption of the Mn will depend strongly on the environment. Thus it's important to know what material the Mn is embedded in. Cheers, John Rehr

Hi ,

I'm trying to help a collegue who would like to use FEFF to simulate X-ray absorption spectra for a single ion (i.e. Mn+2, Mn+3, Mn+4...) through the Mn L3/L2 edge. Since this is quite different from using FEFF for EXAFS like I'm used to... I could really use some help in figuring out how to accomplish this.

We were also trying to figure out a way to remove the background from his experimental absorption spectra -- can Athena do this (or does Athena only work on EXAFS spectra)? If not, does anyone do this type of thing and have suggestions?

Thanks!!! Sincerely,

Kristine Witkowski Northwestern University

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