NEXAFS spectra for same element with different binding energies

["Siew Wei Goh" <sw.goh@unsw.edu.au>]

Dear FEFF Users,

 

I am attempting to use FEFF8 to simulate S K-edge NEXAFS spectra of some transition metal sulfides.  The S atoms in some of these sulfides exist in more than one environment and have different core electron binding energies.  For example, the S atoms in (Fe,Ni)9S8 are in both [4]- and [5]-coordinate metal atom environments, and are expected to have a S 1s binding energy difference of about 1 eV.  My question is whether I need to enter the different S 1s binding energies for the S atoms in the different environments in order to adequately simulate the experimental spectrum, or whether FEFF8 is able to calculate the binding energy difference relative to the S 1s binding energy for elemental sulfur (2472 eV).  If the latter, where in the output files can the estimated S 1s binding energies be found in order to assess how well they agree with experimental data?

 

I have a related question concerning the Fermi level for the different environments.  The Fermi level should be the same for a given material, but whether the Fermi levels estimated by FEFF8 are the same might depend on the definition for Ef used in the program.  Typically, consistent differences of 0.1-0.2 eV have been obtained for different environments for the same element, and 0.3 eV for different elements, in the same material.  What is the definition used in FEFF8 to estimate Ef?  I have read in the FEFF manual that ?the error in Fermi level position is a few eV?.  I presume that refers only to a systematic error in the absolute value of Ef and not in the relative values of Ef estimated for different environments or for different elements in the same material.   Is that correct?

 

Regards,

 

Siew Wei GOH
School of Chemical Sciences

University of New South Wales

Sydney NSW 2052, Australia

Tel: +61 (2) 9385 5519

email: sw.goh@unsw.edu.au