Dear Ling,

This is more appropriately answered at the totalscattering maillist:
[EMAIL PROTECTED]

I will also post it to the diffpy-users google group in case someone
familiar with that list wants to chime in.

Simon Billinge

On Mon, Jul 28, 2008 at 11:03 AM, Yang, Ling <[EMAIL PROTECTED]> wrote:
> Dear All,
>
> There must be some problem with the mailing list since all my emails didn't
> get through. Hope this one will pass.
>
> Stimulated by the topics on pair distribution functions, can I ask some
> questions here about PDF analysis? What is the proper way of scaling in PDF
> calculation, so that one may obtain the actual structure factor and
> coordination numbers? I used both PDFGetN and PDFGetX to get PDF, and also
> tried to do that by hand. What I found is that however I adjust the
> parameters in both softwares, there is always a scale factor (not equal to
> 1) when one try to refine the obtained G(r) in PDFFit. It seems the scale
> factor is determined by some parameters such as the size of sample and
> vanadium bar, and packing ratios etc, which may not be so accurate when one
> inputs them in PDFGetN.  In order to obtain the right coordination numbers,
> the reduced PDF (G(r)=4pi*rho*r[g(r)-1], according to Egami and Billinge's
> definition) must be properly scaled. The scale factor may be found by
> fitting with known model, but may not be so clear for amorphous or unknown
> materials. Is this scale factor arbitrary, or are there some criteria,
> theoretically or empirically? In other words, how can one normalize the
> scattering intensity to get actual structure factor?
>
> Another thing I found is the current version of PDFGetN does not do Lorch
> correction. I am not sure whether there is a new version.
>
> Thanks very much.
>
> Sincerely,
> Ling Yang
> Bldg. 8610, MS 6494
> Oak Ridge National Laboratory
> Oak Ridge, TN 37830
> Tel: (865)576 4845
> Fax: (865)574 1753



-- 
Prof. Simon Billinge
Applied Physics & Applied Mathematics
Columbia University
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Condensed Matter and Materials Science
Brookhaven National Laboratory
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email: sb2896 at columbia dot edu
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