[Ifeffit] Exafs distance resolution
splash at ace.ulyssis.org
Tue Nov 27 03:44:48 CST 2007
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?
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