[Ifeffit] Odd feff result

[Kropf, Arthur Jeremy]

Scott,

This doesn't seem like too unusual a result to me.  The amp ratio from
feff is more of a qualitative than a quantitative prediction.  Now I am
just making a guess; nevertheless, a boron scattering path will probably
have a significantly higher amplitude at low k compared to a Ni or Fe
scattering path.  This could easily be the cause of the difference you
observe.

Jeremy Kropf

Chemical Engineering Division
Argonne National Laboratory
Argonne, IL 60439

Ph: 630.252.9398
Fx: 630.252.9373
kropf at cmt.anl.gov
 

> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov 
> [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf 
> Of Scott Calvin
> Sent: Friday, March 24, 2006 1:01 PM
> To: XAFS Analysis using Ifeffit
> Subject: [Ifeffit] Odd feff result
> 
> Hi all,
> 
> I just ran a feff calculation using feff6L and got a result 
> that surprised me a little. I was modelling a ferrite with a 
> nickel and boron substituted for iron in a small fraction of 
> sites. Here's part of files.dat:
> 
>      file        sig2   amp ratio    deg    nlegs  r effective
>   feff0010.dat 0.00000     2.706     2.000     3   3.7141
>   feff0011.dat 0.00000    26.472    20.000     3   3.7141
>   feff0012.dat 0.00000     4.038     2.000     3   3.7141
> 
> and the corresponding part of the paths.dat:
> 
>      10    3   2.000  index, nleg, degeneracy, r=  3.7141
>        x           y           z     ipot  label      rleg    
>   beta        eta
>     -3.126710    1.042240    1.042240   1 
> 'Ni    '     3.4567  150.5039    0.0000
>     -1.146460    1.146460    1.146460   3 
> 'O     '     1.9857   58.9923    0.0000
>      0.000000    0.000000    0.000000   0 
> 'Fe    '     1.9857  150.5039    0.0000
>      11    3  20.000  index, nleg, degeneracy, r=  3.7141
>        x           y           z     ipot  label      rleg    
>   beta        eta
>      1.042240   -3.126710    1.042240   2 
> 'Fe    '     3.4567  150.5039    0.0000
>      1.146460   -1.146460    1.146460   3 
> 'O     '     1.9857   58.9923    0.0000
>      0.000000    0.000000    0.000000   0 
> 'Fe    '     1.9857  150.5039    0.0000
>      12    3   2.000  index, nleg, degeneracy, r=  3.7141
>        x           y           z     ipot  label      rleg    
>   beta        eta
>     -1.042240    3.126710    1.042240   4 
> 'B     '     3.4567  150.5039    0.0000
>     -1.146460    1.146460    1.146460   3 
> 'O     '     1.9857   58.9923    0.0000
>      0.000000    0.000000    0.000000   0 
> 'Fe    '     1.9857  150.5039    0.0000
> 
> So here's the question. These three paths are identical 
> except for the identity of one of the scattering atoms. The 
> degeneracy of the path with boron and the path with nickel is 
> the same. Why is the feff amplitude ratio for the 
> boron-containing path higher than that of the 
> nickel-containing path? Shouldn't nickel scatter more 
> strongly? And yes, I double-checked...the potentials are 
> defined correctly in the feff.inp file.
> 
> --Scott Calvin
> Sarah Lawrence College
> 
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
>