:term:`CFOUR_CURVILINEAR <CFOUR_CURVILINEAR (CFOUR)>`
"""""""""""""""""""""""""""""""""""""""""""""""""""""

      Specifies whether or not Hessian matrix is transformed (nonlinearly) to curvilinear internal coordinates. A value of 0 (or OFF) turns the transformation off if the analytic force constants are not available, while it is always performed if CURVILINEAR=1 (or ON). Values higher than 1 (or NO) unconditionally turn the transformation off.(Default: ON if analytic Hessian is available, OFF otherwise).

      * **Type**: :ref:`boolean <op_c_boolean>`
      * **Default**: true

