[Ifeffit] Fwd: scattering amplitude by FEFF and Artemis

[Matt Newville]

Dear Feng,

On 6/28/07, Feng Wang <fwang at phys.ualberta.ca> wrote:
> Thank you, Dr. Ravel,
>
> Could you please just simply tell me the expression for the magnitude of chi
> (q) (labelled as |chi(q)|)? Thank you.

I'm sure you didn't mean to sound so demanding, but perhaps you would
consider following Bruce's suggestion of sending a project file.

For what it's worth (in case you missed it while you were reading the
docs and tutorials),
  |chi(q)| = magnitude of the complex chi(q) = FT^(-1) [ chi(R) * Window(R) ]

where Window(R) is a Windowing function and chi(R) = FT[ chi(k) * k^w
* Window(k) ]
where Window(k) is a Windowing function and w is the k-weighting.
Both FT's are band-limited (Rmin,Rmax, and kmin,kmax, respectively).
The convention used in Ifeffit is that chi(k) is strictly real.   This
isn't particularly important if you're only interested in the
magnitude.


I thought your original question was about scattering amplitudes....
Are these questions related?  I couldn't tell much from the plot you
sent, as I didn't understand what "X Axis Title" or "Y Axis Title"
were meant to represent.    Of course, the "scattering amplitude" f(k)
is not the only factor setting the amplitude of chi(k).

Hope that helps.  If not, please  let us know what the issue is,

--Matt