SPring-8, the large synchrotron radiation facility

Speaker : Keisuke Hatada

Language : Japanese

Affiliation : research fellow、University of Camerino, XAS laboratory

Title : Advantages of the structure fitting of XANES spectra by MXAN, and full potential multiple scattering calculations of XANES for anisotropic systems by FPMS

Abstract :
EXAFS is widely used for structural analysis. The oscillating structure of EXAFS can be explained by single scattering theory as a function of positions of atoms, so that one can perform precise analysis with rather non demanding effort by using program such as GNXAS developed by our group in the Univ. Camerino.
In the case of ultra short measurements or investigation of liquid systems, it is difficult to get the fine structure because the spectra are affected by large statistical errors. Instead, since the structure of the Near Edge spectra is more intense and not affected by large errors , XANES is more appropriate for study of these cases. One can more or less interpret the structure of XANES spectra in the energy region from the edge to 100~200 eV by the multiple scattering theory as a function of the atomic positions, so that XANES becomes a powerful tool as EXAFS for structural investigations. While one dimensional information, namely atom-atom distance, is the main information contained in the EXAFS spectra, XANES structure reflects three dimensional geometrical information around the absorbing atom. Moreover, XANES is sensitive to atomic species, which makes more complicated to analyze the spectra.

We have developed MXAN code in the Frascati group. This program enables us to determine the local structure around the absorbing atom by fitting the XANES spectra based on the Multiple Scattering theory. In this talk, I will first show results of analysis for solutions in order to see the difference between the different approaches of GNXAS and MXAN. Then I will show applications to the cases of metalloprotein and pump&probe time dependent XANES.

The Muffin-tin approximation approximation, based on the use of a spherically averaged potential, fails for low dimensional systems and diamond structures. We have developed a full potential multiple scattering theory beyond the Muffin-tin approximation, and we implemented a code based on this theory called "FPMS". By using this code we obtained better results for such systems. In this talk, I discuss the role of the correction for the Muffin-tin approximation and show the improvements obtained by the theory.

Organizer : Tetsuo Honma, Hiroshi Oji, Masafumi Takagaki, Yitao Cui
Mail : honma@sprong8.or.jp, Oji-h@spring8.or.jp, takagaki@spring8.or.jp, yitaocui@spring8.or.jp
PHS : 3508, 3713, 3497, 3758