Obviously. I was talking about fixing the origin when it is not fixed by symmetry.
By the way, GSAS when generate symmetry from space group symbol provide information about the origin. If the origin is not fixed by symmetry is it clearly stated: For example for P2 "The location of the origin is arbitrary in y" Note that GSAS can handle symbols w/o spaces but not in all cases; e.g. both "P2/n" and "P 2/n" results correct symmetry. HOWEVER "P 2 2 2" and "P222" do not. The later symbol give "P2" symmetry! Anyway before making any conclusions correct space group symbol with properly placed spaces has to be used. Peter Zavalij -----Original Message----- From: Allen Larson [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 31, 2004 11:58 AM To: [EMAIL PROTECTED] Peter Zavalij wrote: > > Bob, > Thank you for the clarification. I never had doubts that GSAS handles fixed origin > issue properly but also never understand how it > is done. This way has one big advantage over user fixed origin -- it yields standard > uncertainties for all atoms and therefore for > all distances, etc. > Peter Zavalij > When there is a 1bar site it is automatically chosen as the origin of the unit cell. Any other choice would require adding a extra shift parameter to the X, Y and Z notation in generation the matrices which perform the symmetry operations. Allen
