[Ifeffit] Amplitude in Artemis

[Kelly, Shelly D.]

Hi Paul,

 

How close are the distances for the 6 ligands?  It is usually not
possible to fit a single peak in the EXAFS spectrum by 6 independent
signals.  It sound like the distribution of distances for these 6
ligands is incorrect.  I suggest that you try to fit just the first peak
with one and then with two different shells with unknown coordination
numbers and distances.  This will give you some more information about
what the data indicate the structure is like.

 

If you send me an artemis file, I'll take a peak at it.

 

Shelly

skelly at anl.gov

________________________________

From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Paul
Sent: Monday, February 27, 2006 6:31 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] Amplitude in Artemis

 

Hi Shelly

 

Unfortunately the coordination number is 1 for all atoms present. I have
the crystal structure of the complex, so I am currently including 6
ligating atoms all at distances defined by the structure in the input
file. It seems to be the first shell that is causing the problems, with
a quickfit first shell artemis fit giving nominally 13 ligating species
(which is of course absurd). So I believe something else must be the
problem.

 

Cheers

 

Paul

	----- Original Message ----- 

	From: Kelly, Shelly D. <mailto:SKelly at anl.gov>  

	To: XAFS Analysis using Ifeffit
<mailto:ifeffit at millenia.cars.aps.anl.gov>  

	Sent: Tuesday, February 28, 2006 12:55 AM

	Subject: RE: [Ifeffit] Amplitude in Artemis

	 

	Hi Paul,

	 

	It seems possible that one of the other amplitude terms is also
incorrect.  Scott already mentioned the step height but what about the
coordination number?  The amplitude of the model is given by
coordination number * S02.  You mentioned that the S02 value was
somewhere between 2 and 4.  What is the value for coordination number *
S02?  If the coordination number is 1, then it is possible that the
parameters are switched.  Maybe the coordination number should be
between 2 and 4 and S02 should be around 1.

	 

	HTH,

	Shelly

	 

	
________________________________


	From: ifeffit-bounces at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Paul
	Sent: Sunday, February 26, 2006 6:52 PM
	To: ifeffit at millenia.cars.aps.anl.gov
	Subject: [Ifeffit] Amplitude in Artemis

	 

	I have just started a PhD and have been given alot of EXAFS data
to simulate but I don't know much about artemis. I have tried to fit the
data for quite some time now, but can't get any kind of good fit unless
the amplitude is above 1. Is there any way amp can be above 1 and
rationally explained?

	 

	Cheers,

	 

	Paul

	
________________________________


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