RE: Size Strain in GSAS

[Von Dreele, Robert B.]

Title: Message

A word from a "provider" of a Rietveld code (please don't call me a "programmer"). "But if c>0.4 any pV fails" - OK, for what fraction of the universe of "real world" samples is "c">0.4? I suspect, given the general success of the TCH pseudoVoigt function, that it is exceedingly small and only occurs when one works hard to deliberately make a sample like that.     R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814   -----Original Message----- From: Nicolae Popa [mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 7:14 AM To: [EMAIL PROTECTED] Cc: rietveld_l@ill.fr Subject: Re: Size Strain in GSAS >Dear Nicolae, >Maybe ya ploho chitayu i ploho soobrazhayu, but even after your >explanation I can't see a way to calculate <R> from the results of >fitting described in chapters 6 & 7 of JAC 35 (2002) 338-346. From such >fitting you obtain only dispersion parameter c. Or I missed something? >Anyway, being "Rietvelders" we still have to deal with TCH-pV function >and we need to extract as much as possible correct information from it. >Hope we shall see more appropriate functions for microstructure >analysis in popular Rietveld programs. >Cheers, >Leonid Dear Leonid,   Indeed you missed something. I presume you have the paper. Then, take a look to the formula (15a). This is the size profile for lognormal. There is the function PHI - bar of argument 2*pi*s*<R>.  Replace this function PHI - bar from (15a) by the _expression_ (21a) with the argument x=2*pi*s*<R>. You get it? So, not only "c" but also <R>.   "We are Rietvelders" means that we must be only "codes drivers", "cheffeurs des codes", "voditeli program"? Have we to accept the "Procust bed" of the Rietveld codes at a given moment? All Rietveld codes are improving in time, isn't it?   In particular for the Round_Robin sample TCH-pV works because c=0.18. (Davor explained how Dv and Da are found). But if c>0.4 any pV fails.   Best wishes,   Nicolae