Dear all, I am doing model fitting using Artemis. My sample is uranium solution with an ionic liquid, 1-methoxyethyl-3-methyl imidazolium tetrafluoroborate (MOEMIMBF4). The Fitting seems ok except that the ss_2 is negative. I don't know how can I fix this problem. Can you get a chance to take a look? My fitting is simple, only three single scattering pathes which were produced by Six Pack. The fitting file is attached. I really appreciate it if you could take a look and give some advice! Best regards! Hao
On Friday 23 February 2007 16:24, hw26@njit.edu wrote:
I am doing model fitting using Artemis. My sample is uranium solution with an ionic liquid, 1-methoxyethyl-3-methyl imidazolium tetrafluoroborate (MOEMIMBF4). The Fitting seems ok except that the ss_2 is negative. I don't know how can I fix this problem. Can you get a chance to take a look? My fitting is simple, only three single scattering pathes which were produced by Six Pack. The fitting file is attached. I really appreciate it if you could take a look and give some advice!
Let me ask you a couple questions that I think are closely related to yours. You seem to be modeling an uranyl ligand and two equatorial ligands. Focussing on the second path, the one with a negative sigma^2 and the one that (I am guessing) represents either a hydration shell or a bidentate ligand: 1. Is 35.996 a reasonable value for e0? 2. Is 2.59 Angstrom a reasonable value for an equatorial oxygen ligand in a uranyl moiety? It would seem that your fit has quite a few problems beyond the sigma^2 value. I question whether your parameterization of these three paths is physically defensible. B -- Bruce Ravel ---------------------------------------------- bravel@anl.gov Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007 Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793 My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/
Dear all,
Thanks for reply promptly! First I have to say sorry since I am a new guy in
this filed I may ask some stupid questions. But I am really glad there is such
a great platform where I can get advice and learn from experts and scientists.
Yes, I am modeling the uranyl ligand and two equatorial ligands, one of which
is hypothesized as U-F (from BF4 anion), and the other as U-O (from
hydration),because in the uranyl nitrate standard sloution(without MOEMIMBF4),
there is only one peak that represents the U-O equatorial ligand, but with the
MOEMIMBF4, the equatorial peak is split to two peaks. So I guess the other
equatorial U-F formed.
In the literature, the R for mondentate U-F is 2.24, bidentate is about 2.35;
the R for mondentate U-O is 2.41, bidentate is about 2.54. So I choose 2.24
for U-F and 2.42 for U-O in the path. In the first run, I only set the number
of axial oxygen as 2 (n0), and guess all other parameters. After obtaining
parameters from the first run, I fixed some parameters(especially the
parameters for axial ligand) , and modify others. However, the sigma^2 is
negative, and the enot_2 is too large. In addition, the dr_1 and dr_2 also
seem too large compared with the R from literature. But if I force sigma^2 to
be positive and e_2 to be below 10 ev, the R-factor will increase and the
fitting doesn't seem good.
As for the 2.59 Angstrom for equatorial U-O, it is even a little bit larger
than the bidentate U-O. I don't think it resonable either, since there is no
ligand here that can form the bidentate U-O. Also, the 2.44 Angstrom for U-F
is quite larger than 2.24 from literature, even larger the 2.35 Angstrom for
the bidentate. I don't know if this is due to wrong modeling or because of
some unique characteristcs of ionic liquid.
Best regards!
Hao
Quoting Bruce Ravel
I am doing model fitting using Artemis. My sample is uranium solution with an ionic liquid, 1-methoxyethyl-3-methyl imidazolium tetrafluoroborate (MOEMIMBF4). The Fitting seems ok except that the ss_2 is negative. I don't know how can I fix this problem. Can you get a chance to take a look? My fitting is simple, only three single scattering pathes which were
On Friday 23 February 2007 16:24, hw26@njit.edu wrote: produced
by Six Pack. The fitting file is attached. I really appreciate it if you could take a look and give some advice!
Let me ask you a couple questions that I think are closely related to yours. You seem to be modeling an uranyl ligand and two equatorial ligands. Focussing on the second path, the one with a negative sigma^2 and the one that (I am guessing) represents either a hydration shell or a bidentate ligand:
1. Is 35.996 a reasonable value for e0? 2. Is 2.59 Angstrom a reasonable value for an equatorial oxygen ligand in a uranyl moiety?
It would seem that your fit has quite a few problems beyond the sigma^2 value. I question whether your parameterization of these three paths is physically defensible.
B
-- Bruce Ravel ---------------------------------------------- bravel@anl.gov
Molecular Environmental Science Group, Building 203, Room E-165 MRCAT, Sector 10, Advanced Photon Source, Building 433, Room B007
Argonne National Laboratory phone and voice mail: (1) 630 252 5033 Argonne IL 60439, USA fax: (1) 630 252 9793
My homepage: http://cars9.uchicago.edu/~ravel EXAFS software: http://cars9.uchicago.edu/~ravel/software/
_______________________________________________ Ifeffit mailing list Ifeffit@millenia.cars.aps.anl.gov http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
Dear Hao: Just looking at your fit results, I noticed that enot_2 is also much too large at 35 eV and the dr_2 value is also quite large. Whay are you setting these parameters to such large values? Did you extract them from something else? Cheers, Carlo On Fri, 23 Feb 2007, hw26@njit.edu wrote:
Dear all,
I am doing model fitting using Artemis. My sample is uranium solution with an ionic liquid, 1-methoxyethyl-3-methyl imidazolium tetrafluoroborate (MOEMIMBF4). The Fitting seems ok except that the ss_2 is negative. I don't know how can I fix this problem. Can you get a chance to take a look? My fitting is simple, only three single scattering pathes which were produced by Six Pack. The fitting file is attached. I really appreciate it if you could take a look and give some advice!
Best regards! Hao
-- Carlo U. Segre -- Professor of Physics Associate Dean for Special Projects, Graduate College Illinois Institute of Technology Voice: 312.567.3498 Fax: 312.567.3494 segre@iit.edu http://www.iit.edu/~segre segre@debian.org
In addition to the problems mentioned by Bruce and Carlo, I see that number
of independent data points is 13.8 and numbers of variable is 14. So you are
really using the "+1" factor in your favor here. For the fits to make
physical sense, try to constrain your model such that the number of
variables are about 2/3rd the number of independent data points (as
mentioned by Scott on this mailing list earlier).
As far as the negative ss value is concerned, you can force it to be
positive by setting the path parameter to return positive values only.
Please look into Feffit documentation for the same.
Hope That Helps
Bhoopesh
On 2/23/07, hw26@njit.edu
Dear all,
I am doing model fitting using Artemis. My sample is uranium solution with an ionic liquid, 1-methoxyethyl-3-methyl imidazolium tetrafluoroborate (MOEMIMBF4). The Fitting seems ok except that the ss_2 is negative. I don't know how can I fix this problem. Can you get a chance to take a look? My fitting is simple, only three single scattering pathes which were produced by Six Pack. The fitting file is attached. I really appreciate it if you could take a look and give some advice!
Best regards! Hao
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participants (4)
-
Bhoopesh Mishra -
Bruce Ravel -
Carlo Segre -
hw26＠njit.edu