How to define symmetry?

[Daniel John Rigden <>]

Dear Modellers

I'm trying to build a dimer, constraining the two monomers to be
identical.  From the manual this seems reasonably straightforward but I
can't get it to work.

My current idea is to include the commands in the 'special_restraints'
subroutine (in __special.top), which gets called by __homscr.top after the
other restraints subroutines, thus

SUBROUTINE ROUTINE = 'special_restraints'

# Try to put symmetry restraints here 
# This is called from __homcsr after other restraints set up

       SET ATOM_TYPES = 'ALL'
       SET SELECTION_STATUS = 'INITIALIZE'
       SET SELECTION_SEARCH = 'SEGMENT'

       SET SYMMETRY_WEIGHT = 5.0
       PICK_ATOMS PICK_ATOMS_SET = 2, SELECTION_SEGMENT = '1:' '89:'
       PICK_ATOMS PICK_ATOMS_SET = 3, SELECTION_SEGMENT = '90:' '178:'
       DEFINE_SYMMETRY ADD_SYMMETRY = on off

  RETURN END_SUBROUTINE

I know that this subroutine is read but I never see any indication of
symmetry having been set up when I read the logfile.

What am I doing wrong?

Thanks in advance

Daniel Rigden