Brian, Your definition of Z makes perfect sense (not counting molecular crystals). Except it's better to include partially occupied sites too assuming ( for Z calculation only) that they are fully occupied. For molecular crystals it's more complicated as distance should be calculated to account for molecules residing in special positions.
Peter Zavalij X-ray Crystallographic Center University of Maryland College Park, MD Office: (301)405-1861 Lab: (301)405-3230 Fax: (301)314-9121 From: Brian Toby [mailto:brian.t...@anl.gov] Sent: Wednesday, December 02, 2009 4:47 PM To: Irvin Telepeni; rietveld_l@ill.fr; Leopoldo Sescun Subject: Re: fractional occupancy and composition within GSAS The short answer here is read the code that does this, which I have not done anytime recently. What I recall is the unit cell composition is simply the sum of site multiplicities times the fractional occupancy for each site grouped by atom type. The way I come up with z is something of a kludge -- I think I look for the largest integer divisor for all the non fractionally occupied sites. If anyone has a better suggestion on how to do this, I'd like to hear it. Brian Sent via BlackBerry from T-Mobile _____ From: Irvin Telepeni <irvin.telep...@nottingham.ac.uk> Date: Wed, 02 Dec 2009 17:07:02 +0000 To: <rietveld_l@ill.fr> Subject: fractional occupancy and composition within GSAS Hi, I'd like to know how GSAS (EXPGUI) calculates the atomic composition (through the RESULTS menu) of one phase with respect to the atomic fractional occupancy? How can I get to the same composition values from my fractional occupancies? Cheers, Irvin This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation. No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.426 / Virus Database: 270.14.91/2541 - Release Date: 12/02/09 19:43:00
