[Ifeffit] Re: ? about l_scmt etc.

[Matt Newville]

Hi Kristine, 

> This is actually a feff.inp question.... but I'm hoping someone
> might be able to clarify this for me...
 
I hope someone can provide better insight for Feff8, but here's
what I'd say:

> I was wondering what appropriate values are for l_scmt, l_fms,
> and stoichiometry for the feff.inp I'm working with regarding Au
> on a Ni surface (I'm fitting with feff calculations with either
> a single Au atom in the first Ni layer or two Au atoms in the
> first Ni layer)?
>
> Should they all be the same for each potential?

For EXAFS and EXAFS fitting, the FMS and XANES calculations should
not be done.  For EXAFS, these values don't matter (I think!).  
For what it's worth, L_fms basically sets how high in k the FMS
approach works well enough to use. It's typically a number <~ 5.  
I'm not sure what l_scmt is...

> (i.e. in the past I have used the following for 2 Au's in the surface)
> POTENTIALS
> *     ipot     z     element     l_scmt     l_fms     stoichiometry
>        0        79    Au            3             3           0.001
>        1        28    Ni             2             2           4
>        2        79    Au2           3            3           4

Oh, I think those might be 
       ipot     z    element     lmin   lmax  

and that lmin=-1, lmax=3 are reasonable default values.  Hopefully 
someone can clarify this....

> Oh... one more question... I haven't been using the ellipticity
> card in the feff.inp file, even though I've been using
> "POLARIZATION 1 0 0"... is this OK?

Yes, the ellipticity card is for describing polarizations that are
not linear, such as for magnetic circular dichroism.  For your
surface EXAFS experiments at APS 5-ID, the x-rays were highly
linearly polarized.

Hope that helps, 

--Matt