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 500 West 120th Street Room 200 Mudd, MC 4701 New York, NY 10027 Tel: (212)-854-2918 Condensed Matter and Materials Science Brookhaven National Laboratory P.O. Box 5000 Upton, NY 11973-5000 (631)-344-5387 email: sb2896 at columbia dot edu home: http://nirt.pa.msu.edu/
