Advice #1:

These are from the Internal Option Reference and they might help you. All you have to do is add the IOp(s) to the command line like so: IOp(2/15=4,2/16=3)

IOp(2/15)

SYMMETRY CONTROL.

-1 Turns on symmetry; same as 0 for molecules but turns on assignment of space group ops. for PBC.

0 Leave symmetry in whatever state it is presently in.

1 Unconditionally turn symmetry off. Note that symm is still called, and will determine the framework group.

However, the molecule is not oriented.

2 Bring the molecule to a symmetry orientation, but then disable further use of symmetry.

3 Don't even call symm.

4 Call Symm once with loose cutoffs, symmetrize the resulting coordinates, then confirm symmetry with tight cutoffs.

5 Recover the previous symmetry operations from the rwf, and confirm that the new structure has the same symmetry.

6 Same as 5, but get symmetry info from the chk.

00 Default (10)

10 Do re-orientation for PBC.

20 Suppress re-orientation for PBC.

100 Turn on symmetry operations for PBC.

IOp(2/16)

action taken if the point group changes during an optimization.

0 Abort the job.

1 Keep going.

2 Keep going and leave symmetry on, using the old symmetry.

3 Keep going and leave symmetry on, using the new symmetry.

Advice #2:

You must also remember to use z-matrix instead of Cartesian coordinates, and also apply opt=z-matrix

Thank you.

1. Open your molecule in gaussview.

2. Right click in the drawing window.

3. select edit (gaussview 5) or tools (gaussvies 6) and click point group.

4. Click enable point group and then constraint to subgroup and select the proper subgroup.

5. Click always track point group symmetry.

6. Click ok

7. Run optimisation as usual.