# Example: Spin-flip excitation energies: SiH2¶

Download SiH2_spinflip.run

#!/bin/sh

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

$ADFBIN/adf <<eor Title spin-flip excitation energies of SiH2 Atoms Zmatrix Si 0 0 0 H 1 0 0 1.5145 H 1 2 0 1.5145 92.68 End excitations lowest 20 end unrestricted charge 0 2 SFTDDFT FORCEALDA TDA Basis Type TZ2P End eor mv TAPE21 SiH2_spinflip.t21 rm logfile # 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.$ADFBIN/adf <<eor
Title excitation energies of SiH2
Atoms Zmatrix
Si 0  0  0
H  1  0  0  1.5145
H  1  2  0  1.5145  92.68
End

excitations
lowest 20
end

Basis
Type TZ2P
End

eor
mv TAPE21 SiH2_excit.t21
rm logfile

# 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.