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
