Re: [Ifeffit] Silent Oxygen

[Fuxiang Zhang]

Dear Bruce and Robert,
Thank you very much for the help.

Fuxiang

On Tue, Apr 18, 2017 at 9:10 PM, Robert Gordon 
wrote:

> Hi Fuxiang,
>
> Further to Bruce's note, I looked at your file. Your model splits the
> nearest oxygens by only 0.01A.
> Is that the magnitude of splitting you anticipate?
> Are you familiar with the resolution criteria for EXAFS?
> (k-range [deltak]) * (R-resolution [deltaR]) ~ pi/2 for identical near
> neighbours
> This is also discussed in the archives, e.g.:
> http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2007-Nove
> mber/003414.html
>
> Looking at your chi(k), it seems usable, charitably, up to about 8 A-1,
> not to 12 A-1 as your
> window suggests you have used. Claims of being able to resolve small
> splittings
> with this data will be viewed with skepticism.
>
> -R.
>
> On 4/18/2017 11:34 AM, Bruce Ravel wrote:
>
>> On 04/18/2017 11:10 AM, Fuxiang Zhang wrote:
>>
>>> Hi, all,
>>> I am in studying the EXAFS of perovskite and clearly see the split of
>>> the first peak after ion irradiation. It should come from a symmetry
>>> change, so I use a tetragonal model (instead the original cubic) which
>>> contains two independent O sites. However, after running Atoms and
>>> Feff, all paths are contributed by only one O atom and nothing related
>>> to another Oxygen atoms (see attached file). As a result it may
>>> be difficult to get a good fit of the first split Ta-O peaks. I am not
>>> sure if it is true or something wrong.
>>> Thank you very much
>>>
>>
>> A fairly common question here on the mailing list.  This is a *feature*
>> of Artemis, not a bug.
>>
>> http://bruceravel.github.io/demeter/documents/Artemis/extended/fuzzy.html
>>
>> If you want to /model/ a split in distance, you can drag that path into
>> the path list twice and adjust the delta R and amplitude parameters
>> accordingly.
>>
>> B
>>
>>
>>
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Re: [Ifeffit] Silent Oxygen

[Robert Gordon]

Hi Fuxiang,

Further to Bruce's note, I looked at your file. Your model splits the 
nearest oxygens by only 0.01A.

Is that the magnitude of splitting you anticipate?
Are you familiar with the resolution criteria for EXAFS?
(k-range [deltak]) * (R-resolution [deltaR]) ~ pi/2 for identical near 
neighbours

This is also discussed in the archives, e.g.:
http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2007-November/003414.html

Looking at your chi(k), it seems usable, charitably, up to about 8 A-1, 
not to 12 A-1 as your
window suggests you have used. Claims of being able to resolve small 
splittings

with this data will be viewed with skepticism.

-R.

On 4/18/2017 11:34 AM, Bruce Ravel wrote:

On 04/18/2017 11:10 AM, Fuxiang Zhang wrote:

Hi, all,
I am in studying the EXAFS of perovskite and clearly see the split of
the first peak after ion irradiation. It should come from a symmetry
change, so I use a tetragonal model (instead the original cubic) which
contains two independent O sites. However, after running Atoms and
Feff, all paths are contributed by only one O atom and nothing related
to another Oxygen atoms (see attached file). As a result it may
be difficult to get a good fit of the first split Ta-O peaks. I am not
sure if it is true or something wrong.
Thank you very much


A fairly common question here on the mailing list.  This is a 
*feature* of Artemis, not a bug.


http://bruceravel.github.io/demeter/documents/Artemis/extended/fuzzy.html

If you want to /model/ a split in distance, you can drag that path 
into the path list twice and adjust the delta R and amplitude 
parameters accordingly.


B




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Re: [Ifeffit] Silent Oxygen

[Bruce Ravel]

On 04/18/2017 11:10 AM, Fuxiang Zhang wrote:

Hi, all,
I am in studying the EXAFS of perovskite and clearly see the split of
the first peak after ion irradiation. It should come from a symmetry
change, so I use a tetragonal model (instead the original cubic) which
contains two independent O sites. However, after running Atoms and
Feff, all paths are contributed by only one O atom and nothing related
to another Oxygen atoms (see attached file). As a result it may
be difficult to get a good fit of the first split Ta-O peaks. I am not
sure if it is true or something wrong.
Thank you very much


A fairly common question here on the mailing list.  This is a *feature* 
of Artemis, not a bug.


http://bruceravel.github.io/demeter/documents/Artemis/extended/fuzzy.html

If you want to /model/ a split in distance, you can drag that path into 
the path list twice and adjust the delta R and amplitude parameters 
accordingly.


B


--
 Bruce Ravel   bra...@bnl.gov

 National Institute of Standards and Technology
 Synchrotron Science Group at NSLS-II
 Building 743, Room 114
 Upton NY, 11973

 Homepage:http://bruceravel.github.io/home/
 Software:https://github.com/bruceravel
 Demeter: http://bruceravel.github.io/demeter/
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