Hi, Some of the Shkl values for the Stephens' anisotropic broadening can be negative. However, negative S400, S040 & S004 terms have no physical meaning; best is to probably set them to zero & not refine them further. GSAS has a plotting routine (coupled to gnuplot) that displays the microstrain surface that corresponds to the set of Shkl values obtained in your refinement. Best, Bob Von Dreele
________________________________ From: Franz Werner [mailto:[EMAIL PROTECTED] Sent: Fri 1/11/2008 11:55 PM To: rietveld_l@ill.fr Subject: Stephen's anisotropic microstrain parameters in GSAS Dear All My questions concerns Stephen's anisotropic microstrain parameters in GSAS' profile function no. 4. Are negative values of these parameters (Shkl)) acceptable, i.e. do they have any physical/chemical meaning? In case negative values are not "allowed", how should one proceed (e.g. fix the ill parameters to 0?)? Thanks for your advice. Franz Werner -- Psssst! Schon vom neuen GMX MultiMessenger gehört? Der kann`s mit allen: http://www.gmx.net/de/go/multimessenger?did=10
