[Ifeffit] synthesis of EXAFS via larch

Matt Newville newville at cars.uchicago.edu
Tue Mar 20 13:35:52 CDT 2018

Hi Katy,

On Tue, Mar 20, 2018 at 11:34 AM, Katy Smith <katy.g.smith at gmail.com> wrote:

> I seem to be able to make some progress in using Larch, thanks to the
> developers. I wish to produce a plot in R rather than k, what would be the
> equivalent commands to ff2chi, path.k etc as per the
> /examples/feffit/doc_feffdat3.lar?

The sum with `ff2chi` only sums in k-space.  But the output is ready to do
a Fourier transform with `xftf` (short for "XAFS Fourier Transform
Forward").  So, building on doc_feffdat3.lar,  you could do

   # sum of paths (assumed to be defined already), writing chi(k) to
   ff2chi([path1, path2, path3, path4, path5], group=mysum)

   # now do an XAFS Fourier transform on that group to go from k to R space:
   xftf(mysum,   kweight=2,  kmin=3, kmax=15, window='kaiser', dk=4)

  # plot of |chir(R)| for this sum
  plot(mysum.r,  mysum.chir_mag, label='sum of paths', xlabel=r'$R
\rm\,(\AA)$',ylabel=r'$|\chi(R)| \rm\,(\AA^{-3})$')

We're working to release the next version of Larch very soon, which
includes common xafs plotting commands so that the
last line there could be written as "plot_chir(mysum, label='sum of

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