[Ifeffit] atoms and the alloys
SCalvin at slc.edu
Sun Nov 13 17:12:50 CST 2005
I'm comparing the answers we just gave. I have almost never used FEFF
for XANES...would you agree that =EXAFS= is insensitive to the
difference between Ni and Cu scatterers (except, of course, for the
structural differences that can be handled by fitting parameters such
as delr, ss, and e0)?
Sarah Lawrence College
>FEFF is very sensitive towards subtle changes in the atom list as caused by
>introducing a vacancy or replacing a Ni by a Cu atom as you describe. Imagine
>an FCC system with 50% atom A and 50% atom B. ATOMS has no a priori knowledge
>how it should distribute A and B in the different shells.
>Unfortunately each of
>the possible combination will give you a slightly (or heavily) different XANES
>ATOMS could use a random number generator to decide how a certain
>point in space
>should be occupied. In the above example it would give each atomic position in
>the AB alloy a 50% chance to be either A or B. This will result in a
>file corresponding to only one of many possible atomic permutations. This
>particular atomic configuration might be close to reality - but it might as
>well be unreasonable.
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