:term:`CFOUR_ANH_SYMMETRY <CFOUR_ANH_SYMMETRY (CFOUR)>`
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      Specifies whether nonabelian symmetry is to be exploited in determining displacements for :term:`CFOUR_ANHARMONIC <CFOUR_ANHARMONIC (CFOUR)>` =VIBROT or VPT2 calculations. If set to NONABELIAN (=0), maximum advantage will be taken of symmetry and the full set of cubic force constants will be generated from a skeleton set by application of the totally symmetric projection operator. If set to ABELIAN (=1), only the operations of the abelian subgroup will be exploited. Note: It is important to point out that the symmetrization currently works only for cubic constants. Therefore, if you require quartic force constants (for frequency calculations), you *must* use the ABELIAN option. Moreover, the latter work for only asymmetric tops and linear molecules.

      * **Type**: string
      * **Possible Values**: ABELIAN, NONABELIAN
      * **Default**: ABELIAN