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The Bilbao crystallographic server might be of some use. (http://www.cryst.ehu.es/) Check for instance the Wykoff splitting when going to a lower symmetry: I4/mcm (140) -> I-4c2 (120) wykoff splitting table: I4/mcm I-4c2 32m -> 16i 16i 16l -> 16i 16k -> 16i 16j -> 16i 16i -> 8e 8e 8h -> 8h 8g -> 8g 8f -> 8f 8e -> 8e 4d -> 4d 4c -> 4b 4b -> 4c 4a -> 4a (Looking at this table, I do not understand the splitting in positions you observe, unless I am missing a transformation somewhere ....) The coset decomposition between the two spacegroup gives a clue of which symmetry element is missing between the two spacegroups: A representative elements of the left cosets of I4/mcm and I-4c2 are 1. x,y,z (of course) 2. (-y,x,z) (a 4 fold along z) HTH Peter ----- Original Message ----- From: Bin Li <[EMAIL PROTECTED]> Date: Wednesday, August 2, 2006 8:48 pm Subject: RE: [ccp4bb]: Question about symmetry relationship > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.ccp4.ac.uk *** > > > Dear BR: > > Thank you for your quick reply. > From my data and my experience I believe my refinement with high > symmetry space group is right. > The problem is that if I assume both structures are right, how I > can > describe the atom site relationship in both structures in terms of > symmetry, such as removing inversion center , or mirror planes. > > By the way, if I transfer my high symmetry space group (I4/mcm) to > lower symmetry space group (I-4c2, which is also a subgroup of > I4/mcm), I got the atom sites of A, B, and D at 4a, 16i, and 8h > sites, respectively, in stead of the one reported in the > literature > (4d, 16i and 8e sites). Is this a problem or not? > I hope I am not confusing you. > Your help is highly appreciated! > > Best Regards! > > Bin Li > > > At 10:24 PM 8/2/2006, you wrote: > >The first thing I would look at is the |E**2-1| number > >in the intensity distributions. > >This should indicate whether centrosymmetric or not. > >0.736 for acentric and 0.968 for centric structures. > > > >If this is not decisive in small molecules, suspicion > >is in order, but w/o more stats it is hard to say. > > > >BR > > > > > >-----Original Message----- > >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On > Behalf Of Bin > >Li > >Sent: Wednesday, August 02, 2006 7:47 PM > >To: [email protected] > >Subject: [ccp4bb]: Question about symmetry relationship > > > >*** For details on how to be removed from this list visit the *** > >*** CCP4 home page http://www.ccp4.ac.uk *** > > > > > > > > > >Dear: > >I have a question about symmetry relationship between two space > groups.>In the literature, there is a compound AB4C2. It was > refined with > >I-4c2 space group and A, B, and C are at 4d, 16i and 8e sites, > respectively.>I got a new compound AB4D2 which can be refined very > well with high symmetry > >space group, I4/mcm. In my compound A, B, and D are 4a, 16l, and > 8h sites, > >respectively. If I draw both structures, they look same, except > some bond > >distances change. > >The high symmetry space group is central symmetry and the another > one in > >non-central symmetry, but both have very similar Wyck positions. > >How do I figure out the symmetry relationship between these two > structures?>Your help is highly appreciated! > >Thank you for your time! > > > >Best Regards! > > > >Bin Li > > > >Bin Li, Ph.D > >Ames Lab., Iowa State University > >Ames, IA, USA >
