Stephen and Kurt, P2/n has a 2-fold axis perpendicular to a glide plane, so it does have fixed points (unlike e.g. R3c).
Best regards, Magnus H. Sørby > -----Opprinnelig melding----- > Fra: Kurt Leinenweber [mailto:[EMAIL PROTECTED] > Sendt: 31. mars 2004 08:55 > Til: [EMAIL PROTECTED] > Emne: Defining the origin of P2/n > > > Stephen, > > I think that P2/n has no fixed points, and in order to keep the whole > structure from shifting along the c-axis, one of the atoms has to be > arbitrarily fixed. GSAS automatically fixes the first atom > z-parameter (was > your atom on the 2-fold symmetry axis?). I remember this from > refining the > structure of high pressure FeTiO3 which had space group R3c. > > - Kurt > > > ------- > > Kurt Leinenweber > Department of Chemistry > Arizona State University > Tempe, AZ 85287-1604 > > Phone: (480)-965-8853 > Fax: (480)-965-2747 > > ------- > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] > Sent: Tuesday, March 30, 2004 11:03 PM > To: [EMAIL PROTECTED] > > > Dear Rietvelders, > > I used GSAS to refine my structure in P2/n, however the program > automatically > fixed the the XYZ positions of the first atom during refinement. To my > surprise, this atom is not seen in the "fixed atom list" in the atom > parameters > menu of GSAS. > > Please advise and many thanks, > > stephen > > > > >
