[Ifeffit] [Ext] Re: Plotting chi(R) from FEFF in XAS Viewer (Larch) with phase correction

[Carlo Segre]

Hi Liam:

I agree with Matt.  I don't find phase corrected plots to be very useful.
Rather, I try to just identify peak positions without trying to interpret
what the half-path length might be.  I leave that for the results of the
fitting.  As a secondary, but perhaps more important point, applying the
phase correction in a plot of the Fourier Transform is only an approximate
calculation because the correct phase shift depends on the identity of the
scattering atom and you don't really know that until you have a path model
in the fitting routines.  Once the fitting is done, then you could in
principle phase correct both the data and fit but why bother?

Carlo

On Tue, Dec 13, 2022 at 4:53 PM Matt Newville <newville at cars.uchicago.edu>
wrote:

> Hi Liam,
>
> Yes,  this is not currently available.  It would not be hard to enable,
> but I am not sure it is a great thing to do. I admit that I sort of find
> that phase-correction plots need a lot of explanation, and so are prone to
> causing confusion.  They might be useful for Pt metal, but they cannot
> really be correct for multi-atomic systems.  Well, I guess "correct" is not
> the only consideration ;).
>
> I guess I would ask if there are suggestions and input from people
> teaching XAFS on whether phase corrections (and probably a handful of other
> "tricks" or analysis variations) are actually useful or just confusing.
>
>
>
>
> On Tue, Dec 13, 2022 at 7:58 AM Liam Nagle-Cocco <lavn2 at cam.ac.uk> wrote:
>
>> Dear all,
>>
>> In Artemis it is possible to plot chi(R) for FEFF-fit, with the phase
>> corrected - i.e. bond length corrected for deltaR. This is shown in this
>> screenshot below ("Use this path for phase corrected plotting"). Is this
>> possible in XAS Viewer?
>>
>>
>> Liam Nagle-Cocco *(he/his)*
>>
>> PhD Student in Condensed Matter Physics | Cavendish Laboratory
>>
>> Welfare Officer 2022-2023 | Jesus College MCR
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>
>
> --
> --Matt Newville <newville at cars.uchicago.edu> 630-327-7411
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-- 
Carlo U. Segre (he/him) -- Duchossois Leadership Professor of Physics
Professor of Materials Science & Engineering
Director, Center for Synchrotron Radiation Research and Instrumentation
Illinois Institute of Technology
Voice: 312.567.3498            Fax: 312.567.3494
segre at iit.edu   http://phys.iit.edu/~segre   segre at debian.org
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