Note

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NOSYM

Suppress the automatic detection of point-group symmetry and set the system’s point group to be \(C_1\).

By default, point-group symmetry is used to identify the irreducible representations of molecular orbitals, atomic vibrations, and many-electron excitations, and to accelerate the construction of the Hessian in FORCE calculations. However, symmetric geometries are allowed small numerical deviations from perfect symmetry, which can sometimes cause errors and premature termination of a calculation.

NOSYM is useful for verifying that point-group symmetries are functioning correctly, but some calculations will take longer to run and calculated states will no longer have symmetry labels.