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


Reply via email to