Symmetry Keyword
Last Update: 12/31/2000

This keyword specifies the uses of molecular symmetry within the calculation. If symmetry is in use, the molecule may be rotated to a different coordinate system, called the standard orientation, before the calculation is performed. Derivatives are then rotated back to the original (Z-matrix) orientation. Orbitals are printed in the standard orientation, and input for properties and background charge distributions is required in the standard orientation.

The NoSymmetry keyword prevents the reorientation and causes all computations to be performed in the Z-matrix orientation. By default, symmetry is used wherever possible to reduce CPU, disk storage, and I/O requirements. Symmetry use can be completely disabled by NoSymm, or modified by the Symm keyword and one or more of the following options:

Int
Enables and NoInt disables use of integral symmetry (use of the “petite list”). Synonymous with Int=[No]Symm.

Grad NoGrad
Disables and Grad enables use of symmetry in integral derivative evaluation.

SCF NoSCF
Disables and SCF enables use of N**3 symmetry in SCF, which is used by default only for GVB calculations. SCF=NoSCF is equivalent to Guess=LowSym and 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.

Int, SCF

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