Well there are no general twinning operators for a monoclinic space
group (e.g. like P3, P4) but there are two special cases which come to mind:
* beta=90 in which case the twinning operator is something like
(h,-k,-l) - pseudo primitive orthorhombic.
* where the monoclinic lattice lengths conspire to make your lattice
pseudo C-centered orthorhombic, in which case the twinning operator is
usually something like (h,k,-h-l) but not necessarily identical to that
depending on your cell.
I've had both of these happen to me.
Best way is to run CNS or mmtbx.xtriage (the latter useful for tests
other than twinning), both of which list the twin operators that they try.
Phil Jeffrey
Princeton, NJ
siva charan wrote:
hello
I have a data set to 2.4 A, which has space group of *P21 *. From the
cumulative intensity distribution graph, indicates that data is
twinned . To run the detwin program in ccp4, one has to know the
twinning operator. Can anybody help me, how can I get the twinning
operator for monoclinic space group. I have checked for twin operators
at http://www.ccp4.ac.uk/dist/html/twinning.html, but there are no
twining operators for monoclinic space group.
regards
siva
