Symmetry Control

Disable Symmetry — Water, RHF/STO-3G

Symmetry is on by default. Use NoSymm true to turn it off. This skips point-group ERI screening and prints all orbital irreps as A (C1 symmetry).

task: RHF STO-3G

GEOMETRY
  O   0.000000   0.000000   0.117369
  H   0.756950   0.000000  -0.469476
  H  -0.756950   0.000000  -0.469476
END

INT
  NoSymm true
END

Notes

  • Symmetry is enabled by default. The detected point group is printed in the job header and used to skip symmetry-equivalent ERI shell quartets during energy, gradient, and Hessian computations.
  • NoSymm true forces C1 symmetry: integrals are computed without point-group screening, and all orbital labels are printed as A.
  • The 8-fold permutational symmetry of ERIs is always applied regardless of NoSymm.
  • Symmetry tolerance is controlled in the SYMMETRY section (Tolerance).

Custom Symmetry Tolerance

SYMMETRY
  Tolerance 0.0001
END

Tighter tolerance requires the geometry to more closely match symmetry elements.