Sorry Allen - I guess this new generation of crystallographers really is as bad as you think!
- Kurt ------- Kurt Leinenweber Department of Chemistry Arizona State University Tempe, AZ 85287-1604 Phone: (480)-965-8853 Fax: (480)-965-2747 ------- -----Original Message----- From: Allen Larson [mailto:[EMAIL PROTECTED] Sent: Wednesday, March 31, 2004 9:33 AM To: [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: > > 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 I am amazed by the flow of miss information that flows on this list whenever an apparent problem with a space group comes up. I am forced to wonder if the correspondents in these exchanges have ever looked at 'The International Tables, Volume A(1983)' or Volume 1(1969) or the earlier volume which dates in the 1930's. Or any of the several other treatises that can also serve as a source for this information. The GSAS package contains a program, SpcGroup, that can be used to list the symmetry operations of any possible string defining a possible space group. In general the space group symbol consists of 2 or more groups of characters delimited by spaces. Please note that the spaces separating axial operations are required in the GSAS interpretation of the space group symbol. Thus 'R3c' must be written as 'R 3 c' or taking advantage of the fact that the lattice type can only occupy one character, 'R3 c', is accepted, but not recommended. I might also note that all of this is based on the use of keyboards in general use in English speaking countries. And I did have no information concerning what you might get using other keyboards. Now for P2/n is a centric space group for which there, in my mind, there exists no reasonable origin choice that the 1bar site. Therefore the software would always choose that for the origin of the unit cell. Allen C. Larson