[Ifeffit] Exafs distance resolution

Frenkel, Anatoly frenkel at bnl.gov
Tue Nov 27 08:30:21 CST 2007

Yes and a very important one - see Ed Stern's talk at the 2001 EXAFS workshop "advanced methods and tricks etc. " 
His talk is online. 


-----Original Message-----
From: ifeffit-bounces at millenia.cars.aps.anl.gov <ifeffit-bounces at millenia.cars.aps.anl.gov>
To: ifeffit at millenia.cars.aps.anl.gov <ifeffit at millenia.cars.aps.anl.gov>
Sent: Tue Nov 27 04:44:48 2007
Subject: [Ifeffit] Exafs distance resolution

Dear all,

Is there a physical limitation determining exafs bond distance resolution?

Very often the equation r = pi / 2 deltak is quoted as a measure for 
bond distance resolution. But as i understand this equation is related 
to the fourier transform traditionally used for exafs analysis.
If exafs fitting is done in k-space, on the raw exafs data without 
applying fourier or any other filtering transformation is there a 
physical limitation determining exafs bond distance resolution? This 
question comes down to the following practical problem. If one has a 
theoretical model developed using computational chemistry that predicts 
two different bond lengths within one shell,  e.g. an octahedral metal 
center surrounded by 6 oxygen atoms and this shell is predicted to be 
split in three subshells for wich the bond length differs only 0.05 
angstroms; and this model can be fit very well in k-space with the 
splitted shell, off course keeping the number of fit parameters below 
the nyquist criterion. Is there in such a case any physical reason not 
to fit the experimental data with the splitted shell , but with an 
averaged 6-atom shell with a larger Debye Waller factor?

Best regards,

Eric Breynaert
Ifeffit mailing list
Ifeffit at millenia.cars.aps.anl.gov

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