[Ifeffit] The difference of EXAFS oscillation when using Athena and when using Larch

[Matt Newville]

Hi Yuji,

On Mon, Apr 17, 2017 at 9:49 AM, Yuji Mahara <
mahara.yuji at e.mbox.nagoya-u.ac.jp> wrote:

> Dear All,
>
>
>
> I am Yuji Mahara at Nagoya University, Japan.
>
>
>
> I am using Athena in Demeter 0.9.24 package and Larch 0.9.33 on windows
> 10.
>
> At that time, I am worrying about the difference of EXAFS oscillation when
> using Athena and when using Larch.
>
>
>
> k3-weighted Pd K-edge EXAFS and Fourier transform EXAFS spectrum for PdO
> bulk are shown in attached file(PdO.png).
>
> When XAFS raw data is read using Athena and EXAFS oscillation is obtained,
> EXAFS spectrum is smooth and noise is small. On the other hand, using
> Larch, noise is noticeable in k space.
>
> This phenomenon occurred when analyzing other XAFS data as well.
>
>
>
> I tried to analyze XAFS data by Athena and Larch with the almost same
> conditions.
>
> Does this difference of EXAFS results arise from the difference in
> autobk's algorithm between Athena and Larch?
>
The analysis conditions are shown below.
>
If someone knows this reason, please let me know.
>


There may be subtle differences in the results from autobk() from Ifeffit
and autobk() from Larch, but they should not be very big.   If I recall
correctly, the meaning of the values for the "clamps" is different between
the two, but I don't think that accounts for the changes you're seeing.

Like you say, the differences seem to be more about the noise in the data
which is much more noticeable in the data processed with Larch than with
Athena, as if the data is being smoothed or interpolated differently.  if
the data is very finely spaced or binned in some unexpected way from a
QXAFS collection, that might help explain the difference, though I'm not
sure of that or what behavior would be preferred.

Is it possible to post one of the data files?

--Matt


>
> Best regards,
>
>
>
> Yuji Mahara
>
> ******************************************
> ■ Yuji Mahara
> Nagoya University(Japan)  D3
> Graduate School of Engineering
> Furo-cho, Chikusa-ku, Nagoya-shi, Aichi, 466-8603, Japan
> ・Phone : +81-52-789-3192
> ・E-mail : mahara.yuji at e.mbox.nagoya-u.ac.jp
> ******************************************
>
>
>
> #####Analysis condition of Athena #####
>
>
>
> e0 à[ set e0 to a fraction of the edge step] à 24355.9037323484
> <%28903%29%20732-3484>
>
> Normalization order: 3
>
> Pre-edge range: from -150 to -60 eV
>
> Normalization range: from 150 to 1100 eV
>
> Rbkg: 1
>
> k-weight used by spline: 2
>
> Spline clamp: low=None, high=Strong
>
> Spline range in k: from 0 to 17
>
> Fourier transform k-range: from 3 to 15, dk=0.5, window=’hanning’
>
>
>
> #####Analysis condition of Larch #####
>
>
>
> dat.e0 = 24355.9037323484 <%28903%29%20732-3484> ß e0 was estimated by
> Athena
>
> pre_edge(dat.e, dat.mu, group=dat, e0=dat.e0, pre1=-150, pre2=-60,
> norm1=150, norm2=1100, nnorm=2, _larch=mylarch)
>
> autobk(dat.e, dat.mu, group=dat, e0=dat.e0, rbkg=1, nclamp=5, clamp_lo=0,
> clamp_hi=24, kstep=0.05, kmin=0, kmax=17, kweight=2, win='hanning',
> _larch=mylarch)
>
> xftf(dat.k, dat.chi, group=dat, kmin=3, kmax=15, dk=0.5, window='hanning',
> kweight=3, _larch=mylarch)
>
>
>
> #########################
>
>
>
>
>
>
>
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