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Hello,
if I understand well you study the K-edge absorption spectrum of an element.
This spectrum is essentially due to intense dipolar transition from the core 
1s
level of the element to empty states of p symmetry above the Fermi level. The
transition become possible from a particular energy (edge of the spectrum),
because transitions to empty states are only possible. In the case of Mn the
edge is about 6540 eV. The edge position depends on the oxidation state of the
element and it is different in different materials. For example for Mn the 
edge
position is 6540 eV and this position slightly changes (difference is a few 
eV)
in different materials.
So to calculate the XANES spectrum you should calculate you p-dos above the
Fermi level, and shift the Fermi level position to the edge of the element. 
For
Mn, for example, you calculate the the p-dos of Mn above the Fermi level, you
convolute your calculated dos to a Lorentz function (to take into account
finite life-time of the 1s core hole) or to Gauss function (to take into
account finite resolution of monochromator), and shift your spectrum to 6540
eV.
You can find an example of such calculation in:
A. Titov, X. Biquard, D. Halley et al. Phys. Rev. B 72, 115209 (2005).
For general description of x-ray absorption spectroscopy you can look:
R. Prinz and D. Koningsberger, editors, “X-ray absorption: principles,
applications techniques of EXAFS, SEXAFS and XANES”, J. Wiley and Sons, New
York, 1988.
Best regards,
Andrey Titov.
A.M.Prokhorov General Physics Institute, Moscow