The symmetry of the system is automatically detected. Normally the symmetry of the initial system is maintained. One can lower the symmetry with the Symmetry key. In such cases the keyword POTENTIALNOISE can force the solution away from the initial symmetry.
The most common option is NOSYM forcing the program to run without any symmetry.
It is also possible to run in a lower symmetry other than NOSYM but this is more involved (i.e. for experts only). The argument should be a list of numbers, representing the operators to maintain. The way to proceed is as follows. First run the calculation with the following added to your input
print symmetry
stopafter gemtry
and then you look in the output for (here the first four operators are listed)
64 SYMMETRY OPERATORS:
NO MATRIX TRANSL AXIS DET ROTATION
--------------------------------------------------------------------------
1) 1.000 0.000 0.000 0.000 0.000 1.0 1
0.000 1.000 0.000 0.000 0.000
0.000 0.000 1.000 0.000 1.000
2) 1.000 0.000 0.000 0.000 0.000 1.0 1
0.000 1.000 0.000 5.400 0.000
0.000 0.000 1.000 0.000 1.000
3) 1.000 0.000 0.000 5.400 0.000 1.0 1
0.000 1.000 0.000 0.000 0.000
0.000 0.000 1.000 0.000 1.000
4) 1.000 0.000 0.000 5.400 0.000 1.0 1
0.000 1.000 0.000 5.400 0.000
0.000 0.000 1.000 0.000 1.000
...
from this list you should select the desired operators and use that in your final calculation, for example
Symmetry 1 7 21 31
The initial potential for the SCF procedure is constructed from a sum-of-atoms density. Added to this is some small noise in the numerical values of the potential in the points of the integration grid. The purpose of the noise is to help the program break the initial symmetry, if that would lower the energy, by effectively inducing small differences between (initially) degenerate orbitals. The noise in the potential is randomly generated between zero and an upper limit, which is 1e-4 a.u. by default. The key, which must have a numerical argument, adjusts this upper limit. This can be used therefore to suppress the noise by choosing zero, or to increase it by specifying some large number.
