[Ifeffit] references

[Matt Newville]

Hi Soma,

On Tue, Jan 22, 2013 at 11:11 AM, Soma Chattopadhyay
<soma at agni.phys.iit.edu> wrote:
>
> Hello:
>
> 1) Is there any reference which states what the error bars for Eo, Delr , SS
> and CN should be so that the fit with its parameters  is regarded to be of
> publishable quality?

I don't think one can set a general threshold for what is and is not
publishable according to the size of error bars. Data and results of
analysis need to be of sufficient quality and robustness for the
conclusions drawn.   One can certainly have small error bars and be
wrong!

> 2) A lot of times we find So2 from the respective metal  foil and fix it
> when we fit the sample data for the same element. Is there any reference for
> this one?
>
> I know about the book by Shelly, Hesterberg and Ravel.
> Would appreciate if I get some more references.

I'm not aware of a truly thorough study of this convention. Several of
the early UWXAFS papers mention using this approach.  Probably the
clearest statement is from

  E A Stern, et al "The UWXAFS Analysis Package - Philosophy and Details",
  Physica B208  pp 117-120  (1995)
  [DOI: 10.1016/0921-4526(94)00826-H]

which states (full paragraph):

    The set of parameters that most frequently have a strong
    enough correlation to give difficulty in obtaining their
    values separately are S02, the passive electron overlap
    constant[13], sigma^2, the disorder about the optimal
    distance, and N, the number of atoms in a particular
    coordination shell. The most reliable way to separate out
    sigma^2 from the other two parameters is to measure the
    temperature dependence of sigma^2 and vary the product S02*N
    so as to obtain a fit to an Einstein oscillator, particularly
    the zero point value. Since S02 is dependent essentially on
    only the center atom, it can be found in known structures and
    N determined from the S02*N value.

Here Reference 13 is to Stern and Heald's chapter in the Handbook of
Synchrotron Radiation Vol 1 (1983).

Cheers,

--Matt