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

      Calculation of non-adiabatic coupling. In case of ON (=1) the method by Ichino, Gauss, Stanton is used to obtain the lambda coupling, while in case of LVC (=3) the lambda coupling is computed by means of the algorithm by Tajti and Szalay. Furthermore, NACV (=2) requests the computation of the full non-adiabatic coupling. Note that for calculations using LVC or NACV options the multiroot diagonalization has to be used, as requested via the keyword CFOUR_EOM_NSTATES (dne?) =MULTIROOT.

      * **Type**: string
      * **Possible Values**: ON, NACV, LVC
      * **Default**: OFF

