Re: Rietveld question - GSAS/EXPGUI
> > I would be interested to hear what Brian Toby has to say... Allen Larson wrote: > As Alan notes a space which breaks up the 42/n symmetry operator is disastrous > in the generation of the matrices which define the group. I might also note that > the code recognizes a space as a delimiter in interpreting the group. As for the > fifth field in the space group symbol, the code would never see it. Only 4 > blocks of data, delimited with spaces, are examined by the space group > interpreting code. > > Allen Larson Not much I can add... since Allen wrote the space group interpretation code in GSAS. But, here is a explanation of where to put spaces for GSAS space groups: Space group names specify the symmetry along different directions. The directions themselves depend on the cell class. There should be spaces before and after the symmetry specification for each direction, so P212121 becomes P 21 21 21 and P63/mmc is P 63/m m c. If even this does not mean much to you, you really should borrow a copy of Burns & Glazer's "Space Groups for Solid State Scientists" from your library. Since the GSAS code is quite flexible (for example, it has no problem with the non-standard group F -1), it all too easy to get things wrong. This is why EXPGUI shows you symmetry operators to check against Volume A or the wonderful http://www.cryst.ehu.es/cryst site. This still will not save you from disaster for the cases where the space group can be set with a choice of origin. GSAS, like almost all crystallographic codes, uses the setting with the origin at the centre of symmetry (Origin 2), but many papers have been published using the other choice (Origin 1). If you get this wrong, your computed interatomic distances will be way off, and very likely the density and stoichiometry will be way wrong as well. So, those are good things to check as well. Brian Brian H. Toby, Ph.D.Leader, Crystallography Team [EMAIL PROTECTED] NIST Center for Neutron Research, Stop 8562 voice: 301-975-4297 National Institute of Standards & Technology FAX: 301-921-9847Gaithersburg, MD 20899-8562 http://www.ncnr.nist.gov/xtal
RE: Rietveld question - EXPGUI
The best way is to check generated symmetry operations with International tables for crystallography or on-line using, for example, Bilbao server: http://www.cryst.ehu.es/cryst/get_gen.html which has all conventional and non-conventional settings and much more. Peter Dr. Peter Y. Zavalij University CrystallographerInstitute for Materials Researchand Chemistry DepartmentBinghamton University, SUNY, Vestal Pkwy, EastBinghamton, NY 13902-6000, USATel: (607)777-4298 Fax: (607)777-4623E-mail:[EMAIL PROTECTED]http://materials.binghamton.edu/zavalij -Original Message-From: Nichole Wonderling [mailto:[EMAIL PROTECTED]Sent: Wednesday, March 17, 2004 1:42 PMTo: [EMAIL PROTECTED]Subject: Re: Rietveld question - EXPGUIThank you Peter and Allen. I see that this indeed does make a difference. Can you tell me how I check the space group to ensure that it is correct? As I am not a crystallographer, and have very limited experience with space group terminology, is there a good resource to confirm that I have entered the space group properly? How can I look at the information that pops up in the text box and verify that I have entered the correct information?Again, thanks so much for your help.NicholeAt 12:38 PM 3/17/2004, you wrote: Dear Nichole, Space between 4 and 2 does not make any sense and results in P 4/m m m symmetry. BUT for sure spaces surrounding "/" should be removed and space groups symbol should as following: "P 42/n m c". Note that S is not part of the space group symbol and is probably ignored by GSAS (is it?). Any way both ways (w/ and w/o S) give the same results which corresponds P42/nmc group with the centre of symmetry in the origin. Dr. Peter Y. Zavalij University CrystallographerInstitute for Materials Researchand Chemistry DepartmentBinghamton University, SUNY, Vestal Pkwy, EastBinghamton, NY 13902-6000, USATel: (607)777-4298 Fax: (607)777-4623E-mail:[EMAIL PROTECTED]http://materials.binghamton.edu/zavalij -Original Message-From: Nichole Wonderling [mailto:[EMAIL PROTECTED]]Sent: Wednesday, March 17, 2004 10:50 AMTo: Rietveld ListSubject: Rietveld question - EXPGUI I'm trying to do some refinement on Zr-Y-O powders. I keep getting an error for the space group P 42 / n m c S when I try to import the *.cif file for ICSD 90885 into EXPGUI. Can someone tell me why? Nichole Nichole WonderlingPenn State UniversityMaterials Research Institute159 Materials Research LaboratoryUniversity Park, PA. 16802814-863-1369
Re: Rietveld question - EXPGUI
Thank you Peter and Allen. I see that this indeed does make a difference. Can you tell me how I check the space group to ensure that it is correct? As I am not a crystallographer, and have very limited experience with space group terminology, is there a good resource to confirm that I have entered the space group properly? How can I look at the information that pops up in the text box and verify that I have entered the correct information? Again, thanks so much for your help. Nichole At 12:38 PM 3/17/2004, you wrote: Dear Nichole, Space between 4 and 2 does not make any sense and results in P 4/m m m symmetry. BUT for sure spaces surrounding "/" should be removed and space groups symbol should as following: "P 42/n m c". Note that S is not part of the space group symbol and is probably ignored by GSAS (is it?). Any way both ways (w/ and w/o S) give the same results which corresponds P42/nmc group with the centre of symmetry in the origin. Dr. Peter Y. Zavalij University Crystallographer Institute for Materials Research and Chemistry Department Binghamton University, SUNY, Vestal Pkwy, East Binghamton, NY 13902-6000, USA Tel: (607)777-4298 Fax: (607)777-4623 E-mail:[EMAIL PROTECTED] http://materials.binghamton.edu/zavalij -Original Message- From: Nichole Wonderling [mailto:[EMAIL PROTECTED]] Sent: Wednesday, March 17, 2004 10:50 AM To: Rietveld List Subject: Rietveld question - EXPGUI I'm trying to do some refinement on Zr-Y-O powders. I keep getting an error for the space group P 42 / n m c S when I try to import the *.cif file for ICSD 90885 into EXPGUI. Can someone tell me why? Nichole Nichole Wonderling Penn State University Materials Research Institute 159 Materials Research Laboratory University Park, PA. 16802 814-863-1369
Re: Rietveld question - EXPGUI
Alan Hewat wrote: > > >I'm trying to do some refinement on Zr-Y-O powders. I keep getting an error for > >the space group P 42 / n m c S when I try to import the *.cif file for ICSD 90885 > >into EXPGUI. Can someone tell me why? > > >It seems I may have answered my own question. A space seems to be needed between > >the 4 and the 2. This seems to work. OK? > > I would be interested to hear what Brian Toby has to say, since 42/n is one of the > symmetry elements and I would not expect it to be broken up with spaces (but then I > am not sufficiently familiar with how GSAS does that). I would also be interested to > know what EXPGUI/GSAS does with the trailing S in "P 42/n m c S" since this S is > special to ICSD and means that the axes have been chosen to be not at a center of > symmetry. > > Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]> fax (33) 4.76.20.76.48 > (33) 4.76.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/AlanHewat.htm > ___ As Alan notes a space which breaks up the 42/n symmetry operator is disastrous in the generation of the matrices which define the group. I might also note that the code recognizes a space as a delimiter in interpreting the group. As for the fifth field in the space group symbol, the code would never see it. Only 4 blocks of data, delimited with spaces, are examined by the space group interpreting code. Allen Larson
Rietveld question - EXPGUI
Dear Nichole, Space between 4 and 2 does not make any sense and results in P 4/m m m symmetry. BUT for sure spaces surrounding "/" should be removed and space groups symbol should as following: "P 42/n m c". Note that S is not part of the space group symbol and is probably ignored by GSAS (is it?). Any way both ways (w/ and w/o S) give the same results which corresponds P42/nmc group with the centre of symmetry in the origin. Dr. Peter Y. Zavalij University CrystallographerInstitute for Materials Researchand Chemistry DepartmentBinghamton University, SUNY, Vestal Pkwy, EastBinghamton, NY 13902-6000, USATel: (607)777-4298 Fax: (607)777-4623E-mail:[EMAIL PROTECTED]http://materials.binghamton.edu/zavalij -Original Message-From: Nichole Wonderling [mailto:[EMAIL PROTECTED]Sent: Wednesday, March 17, 2004 10:50 AMTo: Rietveld ListSubject: Rietveld question - EXPGUI I'm trying to do some refinement on Zr-Y-O powders. I keep getting an error for the space group P 42 / n m c S when I try to import the *.cif file for ICSD 90885 into EXPGUI. Can someone tell me why?Nichole
Re: Rietveld question - EXPGUI
>I'm trying to do some refinement on Zr-Y-O powders. I keep getting an error for the >space group P 42 / n m c S when I try to import the *.cif file for ICSD 90885 into >EXPGUI. Can someone tell me why? >It seems I may have answered my own question. A space seems to be needed between the >4 and the 2. This seems to work. OK? I would be interested to hear what Brian Toby has to say, since 42/n is one of the symmetry elements and I would not expect it to be broken up with spaces (but then I am not sufficiently familiar with how GSAS does that). I would also be interested to know what EXPGUI/GSAS does with the trailing S in "P 42/n m c S" since this S is special to ICSD and means that the axes have been chosen to be not at a center of symmetry. Alan Hewat, ILL Grenoble, FRANCE <[EMAIL PROTECTED]> fax (33) 4.76.20.76.48 (33) 4.76.20.72.13 (.26 Mme Guillermet) http://www.ill.fr/dif/AlanHewat.htm ___
Rietveld question - EXPGUI
It seems I may have answered my own question. A space seems to be needed between the 4 and the 2. This seems to work. OK? Nichole Wonderling Penn State University Materials Research Institute 159 Materials Research Laboratory University Park, PA. 16802 814-863-1369
