Example: Excitation energies open shell molecule: CN
****************************************************

"Download CN_unr_exci.run"

   #!/bin/sh


   # Calculation of the excitation energies of the open shell molecule CN

   # In this example, the lowest 20 excitation energies of CN are calculated in a
   # spin-unrestricted TDDFT calculation. In the MO -> MO transitions part for the
   # excitations of the output file, the spin of each molecular orbitals are also
   # specified to help assign the spin state of the excited states. The transitions
   # are always from alpha spin-orbital to alpha spin-orbital or from beta spin-
   # orbital to beta spin-orbital.

   AMS_JOBNAME=exci $AMSBIN/ams <<eor
   System
     atoms
        C  0.0000  0.0000  0.0000
        N  0.0000  0.0000  1.1718
     end
   end

   Task SinglePoint

   Engine ADF
     title excitation energies of CN
     excitations
       lowest 20
       nto
       sfoanalysis
     end
     basis
       type AUG/ADZP
     end
     spinpolarization 1
     unrestricted
   EndEngine

   eor


   # Next the same example for CN is given with the Tamm-Dancoff approximation
   # (TDA) approximation (including TDA in the input). Due to this approximation
   # the calculated excitation energies will not be exactly the same as in the
   # first example.

   AMS_JOBNAME=exci_tda $AMSBIN/ams <<eor
   System
     atoms
        C  0.0000  0.0000  0.0000
        N  0.0000  0.0000  1.1718
     end
   end

   Task SinglePoint

   Engine ADF
     title excitation energies (TDA) of CN
     excitations
       lowest 20
       nto
       sfoanalysis
     end
     basis
       type AUG/ADZP
     end
     spinpolarization 1
     tda
     unrestricted
   EndEngine

   eor


   # Note that the basis set is still far from complete, the ATZ2P is better. For
   # accuracy reasons one may need to increase the numerical quality. If one uses
   # the augmented basis sets for accuracy reasons one could use NumericalQuality
   # Good.

   # The third calculation is the calculation of spin-flip excitation energies for
   # CN. Again these energies will not be exactly the same as in the first example.
   # For open-shell molecules, spin-flip transition can result in transition to the
   # ground state with a different S_z value, while the symmetry of the transition
   # density is A1 (Sigma+ for linear molecules). The excitation energy of this
   # transition should be zero and this can be used to test the reliability of
   # spin-flip TDDFT. Indeed the calculation of the spin-flip excitation energies
   # of CN shows one value which is close to zero and has a transition density of
   # Sigma+ symmetry.


   AMS_JOBNAME=exci_tda_spinflip $AMSBIN/ams <<eor
   System
     atoms
        C  .0000  .0000  .0000
        N  .0000  .0000 1.1718
     end
   end

   Task SinglePoint

   Engine ADF
     title spin-flip excitation energies (TDA) of CN
     excitations
       lowest 20
       nto
       sfoanalysis
     end
     basis
       type AUG/ADZP
     end
     sftddft
     spinpolarization 1
     tda
     unrestricted
   EndEngine

   eor
