[Ifeffit] How to input atoms in solid solution for Artemis

[Fuxiang Zhang]

Thank you all for the help.

Fuxiang

On Thu, Jun 23, 2016 at 10:19 PM, Matt Newville <newville at cars.uchicago.edu>
wrote:

> Fuxiang,
>
>
> On Thu, Jun 23, 2016 at 4:47 PM, Fuxiang Zhang <zhangfx at umich.edu> wrote:
>
>> Hi, Scott,
>>
>> In fact, I have a series of single crystal Ni-Fe alloys (Fm-3m) with
>> known atomic ratio, and measured both Fe and Ni edges for samples and
>> standards. I just want to see if there's any difference between the local
>> bonding environment of Fe and Ni, such as R, N and sigma2. Now using the
>> suggested method by Matt by changing atoms in FEFF.inp file, I can only
>> get ss, deltr and E0 from fitting (I don't know how to refine N and R).
>>
>
> You can refine N and deltaR for any scattering path.  R is Reff + deltaR,
> so that *is* refining R.   When you say "I don't know how to refine N and
> R", I'm left unsure what part you do and do not know. There are lots of
> on-line examples and documentation.  If you're having trouble, it might
> help to ask a specific question.
>
>
>> But the fitting with Ni (or Fe) edge can only generate the same R and
>> deltr for Ni-Ni and Ni-Fe pairs.
>>
>
> I'm sorry, I don't understand.  In principle, the Ni-Ni distance and Ni-Fe
> distances can be different, of course.
>
> Fitting the edges of Ni and Fe will yield a little difference in the R and
>> deltr. Which results should I believe, or something wrong I am using the
>> program because I cannot generate different R for Ni-Ni and Ni-Fe pairs
>> with the same data set.
>> Many thanks for your suggestions and helps.
>>
>
> I can't tell whether you're saying you do not know how to tell Artemis to
> refine different distances for Ni-Ni and Ni-Fe, or that when you do tell it
> to do this that the result is that the two distances are the same.
>
> As said earlier, unless you're looking at some weird situation, I would
> expect measuring distances and coordination numbers separately for Ni-Ni,
> Ni-Fe, Fe-Fe, and Fe-Ni to be very, very hard.   My recollection (could be
> wrong) is that the nominal near-neighbor distances for fcc Ni and bcc Fe
> are both around 2.48 Ang.  With Z different by only 2, I would not expect
> these to be distinguishable.
>
> But the program definitely allow you to try....
>
> --Matt Newville
>
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