Just shift the origin in the C2 group and you get C21. Since they're
redundant, only one is named, the simpler one.
On Tue, 11 Sep 2007, wu donghui wrote:
Dear all,
I just get into touch with x-ray crystallography, and I made a "big"
discovery that there is no C21 space group in monoclinic system, which
system only contains P2, P21 and C2 groups. Even in the entire 65 chiral
space group, there is no space for this group. I made an assumption that if
there is C21 space group in monoclinic system, then the four equivalent
point position could be described as: x, y, z; 1/2+x, 1/2+y, z; -x, 1/2+y,
-z; 1/2-x, y, -z. However when I check the 65 chiral space group, no one is
compatible with this equivalent positions. And I know I must make some
mistakes. Unfortunately I can not find where the mistake stems from. I have
to recourse to our expert community for your generous help.
All replies are warmly welcomed and appreciated.
Best regards,
Donghui
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