[Ifeffit] Amplitude in Artemis

[Paul]

Hi Shelly

I've attached the artemis project files.

Hopefully you get further with them than I have been able to.

Cheers

Paul
  ----- Original Message ----- 
  From: Kelly, Shelly D. 
  To: XAFS Analysis using Ifeffit 
  Sent: Wednesday, March 01, 2006 1:50 AM
  Subject: RE: [Ifeffit] Amplitude in Artemis


  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


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  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. 

    To: XAFS Analysis using Ifeffit 

    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

     


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    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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