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cad in R32/ccp4 asymmetric units
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I am running cad on a data set in the space group R32 and am
wondering why cad does what it does.
For example, input.mtz has these two reflections first:
4 -2 6
4 -1 -7 with a certain F and sigF.
output.mtz (output from cad) has these two reflections first, with the
same F and sigF as the first dataset, so they ought to be equivalent:
2 2 6
3 1 -7 with the same F and sigF
So, the question is, how are these reflections equivalent?
The matrix that transforms a reflection from the first set (hkl) into
the reflection in the second set (HKL) is:
1 1 0
0 -1 0
0 0 1
This isn't one of the symmetry operators for R32. But, if I'm
thinking about this correctly, this matrix transforms in reciprocal
space, so the transpose matrix should apply in real space. The
transpose of that matrix should be:
1 0 0
1 -1 0
0 0 1
But, that's not one of the symmetry operators for R32 either.
The documentation for cad says the following:
2. Unless otherwise instructed, the program places output data in the
CCP4 asymmetric unit (which sometimes differs from that in the
International Tables), and sorts it to a standard order.
So, I'm assuming that cad is putting this into an asymmetric unit which
differs from that in the Tables.
Can anyone tell me what asymmetric unit CCP4 uses for R32? and why?
Thanks for your wisdom!
Erica Ollmann Saphire
- SFALL Bug
- From: "Borhani, David" <email@example.com>