The imaginary frequency due to the reaction vector in a transition state calculation must not be included in the thermochemical calculation. The number of genuine vibrations considered can be: 3N-5 for a linear ground state system, 3N-6 for a non-linear ground state system, or 3N-6 for a linear transition-state complex, 3N-7 for a non-linear transition-state complex.

This keyword must be used in conjunction with THERMO if a transition state is being calculated.