Dear Ramadas, Your problem is that your Si atoms are related by equivalent positions to the ones you need for your restraint. You need to get all of them within bonding distance of each other by transforming them via the symmetry operators. Then angle restraints will be easy. Run disagl to get equivalent positions for the atoms in the angles you want to restrain. Bob Von Dreele
R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -----Original Message----- From: Ramadas Sunil Pophale [mailto:[EMAIL PROTECTED] Sent: Tuesday, December 18, 2007 4:05 PM To: rietveld_l@ill.fr Subject: bond angle restraints Dear GSAS users, May be a tad trivial question. I am refining a structure with 5 SI atoms. I want to include soft restraints, both bond length and bond angle. I can add the bond length restraints easily using expedt. However, run into a small problem while trying to add bond angle restrains. The program asks me to include sequence number for the atoms involved. Since there are 5 I try combinations such as 1-2-3 etc. I get a message saying the bond length of 1-2 is 13 A > 2 A so restraint cannot be added. I know I can change the limit from 2 A to something else, but still this is confusing because when I added the bond restraint, the distance between 1 and 2 was shown to be around 3.147, closer to the expected 3.1 A for Si-Si bond. So I was confused as to why it would be shown to be ~ 13 A the second time around. Thanks in advance for your help. Happy holidays :-) Ramdas.
