[Ifeffit] problem with E0 (enot) parameters
Zajac, Dariusz A.
dariusz.zajac at desy.de
Mon Jun 22 09:44:00 CDT 2009
Hi all,
I had followed your advices and I can shortly summarised what I've got.
I fitted with and without background with feff 6 and feff 8.4. For feff
8.4 I did also with SCF=4.0
I fitted only first two peaks (R(1.7-4A) k(3-15A^(-1)))
for feff 6 and feff 8.4 I had the same values of E0 for N and C, non
using self-consistent potential, using it enot became smaller. All other
parameters are playing around, within th error bars.
fits with bkg and without it have very simnillar results, see below.
more you can find on pictures:
http://yfrog.com/29k4wcn8compbkgpx
http://img81.imageshack.us/i/k4wcn8feff84.png/
_comp_bkg : comparison of different feff fits with bkg
_feff6 : with and without bkg for feff6
_feff8.4 : as above for ver 8.4
cheers
darek
statistical parameters
# Fitting Na2WO4_W_L3.chi
# report on "Statistical parameters"
# -----------------------------------------------------------------
# fit FoM R-factor
Reduced_chi-square Chi-square nvar nidp
'K4W(CN)8 R(1.7-6)' 1 0.0227 14347.765
219223.767 30 45
'K4W(CN)8 R(1.7-4) no bkg' 3 0.0257 18704.721
192125.245 7 17
'K4W(CN)8 R(1.7-4) with bkg' 4 0.0211 32207.729
196737.642 24 30
'K4W(CN)8 R(1.7-4) no bkg feff 8.4' 5 0.0284 18350.504
188486.912 7 17
'K4W(CN)8 R(1.7-4) with bkg feff 8.4' 6 0.0228 29638.929
181046.387 24 30
'K4W(CN)8 R(1.7-4) bkg SCF' 10 0.0251 33785.217
206373.569 24 30
Enot_C
# Fitting Na2WO4_W_L3.chi
# report on "enot_C"
# -----------------------------------------------------------------
# fit FoM enot_C
+/- initial
'K4W(CN)8 R(1.7-6)' 1 12.5967170
0.6539780 12.601228 (0.744286)
'K4W(CN)8 R(1.7-4) no bkg' 3 13.6410110
1.0472200 13.641011 (1.047220)
'K4W(CN)8 R(1.7-4) with bkg' 4 13.5499020
1.7066630 13.549902 (1.706663)
'K4W(CN)8 R(1.7-4) no bkg feff 8.4' 5 16.9324090
0.9260820 16.932409 (0.926082)
'K4W(CN)8 R(1.7-4) with bkg feff 8.4' 6 16.5096270
1.5718970 16.509228 (1.571714)
'K4W(CN)8 R(1.7-4) bkg SCF' 10 4.1640860
1.5582580 4.164119 (1.558271)
Enot_N
# Fitting Na2WO4_W_L3.chi
# report on "enot_N"
# -----------------------------------------------------------------
# fit FoM enot_N
+/- initial
'K4W(CN)8 R(1.7-6)' 1 12.4065290
1.7757010 12.895967 (2.018563)
'K4W(CN)8 R(1.7-4) no bkg' 3 10.5289150
2.3544970 10.528916 (2.354497)
'K4W(CN)8 R(1.7-4) with bkg' 4 10.4310180
3.5828820 10.431018 (3.582882)
'K4W(CN)8 R(1.7-4) no bkg feff 8.4' 5 23.3734610
1.2695440 23.373461 (1.269544)
'K4W(CN)8 R(1.7-4) with bkg feff 8.4' 6 24.5886140
5.7410720 24.590866 (5.737253)
'K4W(CN)8 R(1.7-4) bkg SCF' 10 2.2653510
4.7905060 2.265237 (4.790501)
>-----Original Message-----
>From: ifeffit-bounces at millenia.cars.aps.anl.gov
>[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf
>Of Matt Newville
>Sent: Saturday, June 20, 2009 5:41 PM
>To: XAFS Analysis using Ifeffit
>Subject: Re: [Ifeffit] problem with E0 (enot) parameters
>
>
>Hi Dariusz,
>
>Just to follow up on Stefan's request to not post large
>attachments to email:
>
>The ifeffit web page is a wiki, and would be an ideal place
>for posting the data (feff inputs, project files, images of
>plots) for such questions. You can read up on the wiki page
>for how to do create
>pages and post attachments. I'd encourage anyone with similar
>impulses to post large files to use the wiki for such discussions.
>
>To follow up on the rest of your questions and this thread:
>
>I agree with Jeremy's advice / observation that having an E0
>shift push E0 "over the white line" is not so unusual when
>using Feff6,
>especially for L3 edges. I'm not sure there's a good reason for it
>besides "Feff6 makes approximations".
>
>I'd also add a few other points:
> 1. In your original post, you had a huge number (30!) of
>variables. I'd recommend that you start much more simply than
>that. In particular, I'd suggest starting without refining
>the background.
> 2. As you know, It's hard for EXAFS to distinguish between
>C, N, and O backscatters, and so "flipping atoms" around to
>positions that are "obviously incorrect but consistent with
>the EXAFS data" is something you'll need to look out for,
>especially with so many variables (see point 1).
> 3. My understanding is that W L3 is particularly hard. If
>you haven't already done so, I'd suggest checking the
>literature on this and doing as many sanity checks as possible.
>
>--Matt
>_______________________________________________
>Ifeffit mailing list
>Ifeffit at millenia.cars.aps.anl.gov
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>
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