Example: Spin-flip excitation energies: SiH2
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"Download SiH2_spinflip.run"

   #!/bin/sh


   # Calculation of the spin-flip excitation energies of the open shell molecule SiH2

   AMS_JOBNAME=SpinFlip $AMSBIN/ams <<eor
   System
     atoms
        Si 0.0  0.0                0.0
        H  0.0 -1.095664024353027 -1.045576810836792
        H  0.0  1.095664024353027 -1.045576810836792
     end
   end

   Task SinglePoint

   Engine ADF
     title spin-flip excitation energies of SiH2
     excitations
       lowest 20
     end
     forcealda
     basis
       type TZ2P
     end
     sftddft
     spinpolarization 2
     tda
     unrestricted
   EndEngine
   eor

   # In this example, the lowest 20 spin-flip excitation energies of SiH2 are
   # calculated in a spin-unrestricted TDDFT calculation.

   # In this case an excited state is used as reference, which means that there can
   # also be a negative excitation energy, which is indeed the case. The electron
   # configuration used in the SCF is (a1)^1 (b1)^1, with Sz=1, thus a ^3B_1
   # state, which is an excited state. The ^1A_1 state with electron configuration
   # (a1)^2 is lower in energy, and is the ground state.

   # There is also an excited 1A1 state with electron configuration (b1)^2. The
   # transition from the ground 1A1 state to the excited 1A1 state is an excitation
   # from the electron configuration (a1)^2 to (b1)^2. This transition is actually
   # a double excitation, which means that some double excitations can be reached
   # using spin-flip TDDFT with carefully selected reference states.

   # 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. Note that in these spin-flip calculations the
   # transitions are always from alpha spin-orbital to beta or from beta spin-
   # orbital to alpha spin-orbital.

   # For open-shell molecules, spin-flip transition can result in transition to the
   # ground state with a different Sz value, while the symmetry of the transition
   # density is A1. 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 SiH2 shows one value which
   # is close to zero and has a transition density of A1 symmetry.

   # The 1A1 state with electron configuration (a1)^2 can also be used in the
   # calculation of the excitation energies. This is a closed shell configuration,
   # in which case we do not need the spin-flip method.


   AMS_JOBNAME=Excitation $AMSBIN/ams <<eor
   System
     atoms
        Si 0.0  0.0                0.0
        H  0.0 -1.095664024353027 -1.045576810836792
        H  0.0  1.095664024353027 -1.045576810836792
     end
   end

   Task SinglePoint

   Engine ADF
     title excitation energies of SiH2
     excitations
       lowest 20
     end
     basis
       type TZ2P
     end
   EndEngine

   eor

   # The transition from the ground ^1A_1 state to the excited ^1A_1 state, which
   # is an excitation from the electron configuration (a1)^2 to (b1)^2, can not be
   # reached in this calculation, since it has mainly double excitation character.
   # Of course, other excited ^1A_1 states can be reached.
