xaid_ff
Module characteristics
- Goal:
to calculate the Fourier Transform (FT) of a XAFS spectrum Chi(k)
and the Back Fourier Transform (BFT) of a selected region of the FT. Chi(k) can be weighted with powers
of k (from 0 to 4) and many
weighting windows are available.
- Method: Calculate
the Fast Fourier transform using the ftrset
and fastftr functions
- Input:
A 2 column file with Chi(k)
data. It may also receive data from other XAID
modules.
- Output:
A SPEC-formatted data file with signal, FT and BFT (Use File->Save File).
-
Tricks:
- After changing any
parameter, press "Enter" to refresh calculations.
- The syntax of the
intervals is: [min,max]. The square brackets and the separating coma are
must always be entered.
Example of use
- Load
a 2-colums ASCII file with input data (k
in A in the first column and Chi(k)
in the second one) by using the File->Load File menu. Use for example the
file Ge_calib.chi in the Examples directory of the xaid distribution.
This file is loaded using File->Load Example File
- After loading the data, one gets:

-
Change
Input parameters:
- The k
limits for the FT (in left window)
- The R
interval in central window (limits for the FT plot).
- The R
limits for the Back Fourier (in central window). The BFT is calculated
from the FT within these limits in R.
The selected limits appear as vertical lines in the FT window (central
window). This helps to select more accurately the wanted limits, normally
including one or several peaks in the FT.
- The k
limits for the congugated variable (BFT in the right window). Note that
this interval must be smaller than the "k limits for the Fourier
Transform" interval in the left window, otherwise some numerical
inconsistences appear.
- The "Shell radius
rfor the back phase". This
affects only the BFT phase. The BFT is written as A(k)*sin(2kr+Phi(k)).
The phase is Phi(k)
- Press
Enter
for calculating and updating the windows after entering any new parameter.
Batch calculations
XAID_FF cannot read directly multiple data sets, but it can be done by
calling XAID_FF from DELIA and EXODUS.