[Ifeffit] Query regarding measurement uncertainity

[Matt Newville]

Hi Bindu,

On Mon, Jan 26, 2009 at 8:28 AM, Bindu R. <binduiuc at yahoo.co.in> wrote:
>
> I have one doubt regarding the measurement uncertainty in R- space (εR). In
> the manual it is written that εR is evaluated from the rms value of FT in
> the range 15-20 Å. My doubt is.....
>
> In case the FT in R-space does not extend up to the range mentioned above,
> then how does the fitting program choose the value of εR?
>

The FT transform from k to  R space that ifeffit does always extends
to R = 10*pi Ang.  The R-range saved into a data array is usually much
shorter (it's usually out to 10Ang), though you can change this if
you'd like.   There are always high-frequency components of a real
XAFS spectra.

Anyway, when doing a fit, the data is FT to R-space internally, and
the range between 15 and 20 Ang is used to estimate epsilon_R.
Knowing the FT parameters (especially the k-weight), that can be
converted into epsilon_k.

--Matt