This keyword specifies the uses of molecular symmetry within the calculation. By default, the program attempts to identify the point group of the molecule. If symmetry is in use, the molecule may be rotated to a different coordinate system, called thestandard orientation, before the calculation is performed. Derivatives are then rotated back to the original (input) orientation. Orbitals are printed in the standard orientation. Input for properties and background charge distributions must be specified in the standard orientation.
By default, symmetry is used wherever possible to reduce CPU, disk storage, and I/O requirements. TheNoSymmetrykeyword prevents molecule reorientation and causes all computations to be performed in the input orientation (although the program still attempts to identify the appropriate point group). Symmetry use can be completely disabled bySymmetry=None; use this option ifNoSymmgenerates an error when identifying the point group.
Int
Intenables andNoIntdisables use of integral symmetry (use of the petite list). Synonymous withInt=[No]Symm.
Grad
NoGraddisables andGradenables use of symmetry in integral derivative evaluation.
SCF
NoSCFdisables andSCFenables use of N3symmetry in SCF, which is used by default only for GVB calculations.Symm=NoSCFis equivalent toGuess=LowSymand combining all irreducible representations together.
Loose
Tells the program to use looser cutoffs in determining symmetry at the first point. It is designed for use with suboptimal input geometries.Tightsays to use the regular criteria at the first point, and it is the default.
Follow
Try to follow point group/orientation during optimization.
PG=group
Use no more symmetry than that found in the specified point group.
Axis=[X|Y|Z]
Specify axis to help specify subgroup.
On
Turn on symmetry when it would otherwise be off, such as withMassage. This can cause wrong answers, so it should only be used if you know what you’re doing!
CenterOfCharge
Use the center of atomic charges in determining the standard orientation. This is the default.COCis a synonym for this option.
CenterOfMass
Use the center of atomic masses in determining the standard orientation.COMis a synonym for this option.
None
Do not assign point group and bypass all symmetry processing.
Last update: 23 April 2013