[Ifeffit] to use scattering path in different model or to construct a new model which is the combination of different simple compound

[Bruce Ravel]

On 07/01/2014 10:43 AM, ZHAN Fei wrote:
> 1 In the example,multiplet scattering path comes from two model
> respectively,if use path from different model in different shell's
> fit,there is risk of ignore important multiple path across models.Should
> construct a cluster ,run feff to ensure?

I don't completely understand the question, but I'll give it a try.

In the example of Shelly's paper, she had a situation where she 
*couldn't* write a single feff.inp file.  Her local environment was the 
average of all possible ways that the uranyl ion could bond to biomass. 
  The uranyl binding disproportionated into a pH-dependent mixture of 
carboxyl, phosphoryl, and hydroxyl sites.  There was simply no way to 
write a feff.inp file for that.  So her solution was to run Feff more 
than once, picking and choosing paths that represented her best guess 
for modeling the average bonding environment.

I think what you are really getting at, though, is whether it was right 
for Shelly to use parts of Feff calculations on a crystals to model 
something else.  If you were to read up on the theory used in Feff, you 
would find that the important thing is that the muffin tin radii of the 
scatterers get calculated reasonably.  Unless Shelly had a reason to 
think that the interatomic distances in her biomass sample were VERY 
different than in the crystals she used to run Feff, then the scattering 
amplitudes and phase shifts were almost certainly computed quite well 
enough.

> 2 I have confusion of the relationship pf N between single path and
> multiple path,for example I think U-Oe-C U-Oe-Pshould be 1 2
> respectively,instead 2 4 in paper.

I think Scott's explanation is correct.  In real-space, 
multiple-scattering theory, both ways around a three-legged path have to 
be counted.

B


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  Bruce Ravel  ------------------------------------ bravel at bnl.gov

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