Example: Exciton transfer integrals with FOCDFT¶
Download ExcitonTransfer_FOCDFT.run
#! /bin/sh
# FOCDFT is used to calculate exciton transfer integrals
# for the ethylene dimer and trimer using CIS (HartreeFock with TDA).
# First the isolated fragments are calculated.
# Because in the final complexes the 2 or 3 ethylene molecules are the same,
# only one fragment needs to be calculated.
# For such a small molecule, a relatively small TZP basis set is used, which is
# not sufficient for excitations to Rydberg-like orbitals.
# For larger molecules a TZ2P basis set is in most cases
# sufficient. In that case one might even consider smaller basis sets.
# In a real application one also probably wants to calculate a higher number
# of excitations than that are calculated in this example.
# Next the choice of XC functional is important.
# If FOCDFT is used for the calculation of exciton transfer
# best is to use an XC functional that can reasonably well
# calculate both local excitations as well as charge-transfer excitations,
# like long range-separated functionals.
# For analysis reasons we also do a CIS calculation
# on the ethylene fragment.
# In the calculation D(2h) symmetry is used.
# The B1.u excitation will be a valence excitation, and
# the B3.u excitation will be a Rydberg excitation.
# Note that in D(2h) symmetry the orientation of the molecule
# matters in what is called a B1.u or B3.u excitation, for example.
AMS_JOBNAME=Frag $AMSBIN/ams <<eor
System
symmetrize
atoms
C 0.00000000 0.00000000 -0.66600000
C 0.00000000 0.00000000 0.66600000
H 0.00000000 0.92878500 -1.24030100
H 0.00000000 -0.92878500 -1.24030100
H 0.00000000 -0.92878500 1.24030100
H 0.00000000 0.92878500 1.24030100
end
end
Task SinglePoint
Engine ADF
basis
Type TZP
core none
end
xc
hartreefock
end
TDA
Excitations
Davidson
B1.u 1
B3.u 1
End
Tolerance 1e-5
End
EndEngine
eor
# Next we calculate the full complex of the dimer.
# The key ExcitonTransfer is used such that electronic couplings between diabetic states
# are calculated.
# Note that one should not use symmetry-equivalent fragments in the final complex,
# because we want to localize orbitals on a fragment, which breaks this symmetry.
# In the calculation C(2v) symmetry can stlll be used.
# 'Localize OccupiedOnly' is used, which means that the calculated excitations
# are linear combinations of single-orbital transitions from occupied orbitals
# on one fragment to virtual orbitals on all fragments.
# The subkey descriptors of the block key Excitations is used
# such that the output gives information on the local or charge transfer
# character of these excitations.
# The two lowest localized B1 excitations will be close to the two local B1.u valence excitations
# on either fragment. Likewise the two lowest localized A1 excitations will be close to the
# two local B3.u Rydberg excitations on either fragment.
# The calculated electronic couplings between states of different symmetry will be zero.
AMS_JOBNAME=ET2_excitontransfer $AMSBIN/ams <<eor
System
symmetrize
atoms
C 0.000000 0.000000 0.000000 adf.f=Frag1
C 1.332000 0.000000 0.000000 adf.f=Frag1
H -0.574301 0.000000 -0.928785 adf.f=Frag1
H -0.574301 0.000000 0.928785 adf.f=Frag1
H 1.906301 0.000000 0.928785 adf.f=Frag1
H 1.906301 0.000000 -0.928785 adf.f=Frag1
C -0.000000 4.000000 0.000000 adf.f=Frag2
C 1.332000 4.000000 -0.000000 adf.f=Frag2
H -0.574301 4.000000 0.928785 adf.f=Frag2
H -0.574301 4.000000 -0.928785 adf.f=Frag2
H 1.906301 4.000000 -0.928785 adf.f=Frag2
H 1.906301 4.000000 0.928785 adf.f=Frag2
end
end
Task SinglePoint
Engine ADF
fragments
Frag1 Frag.results/adf.rkf
Frag2 Frag.results/adf.rkf
end
xc
hartreefock
end
TDA
Excitations
Davidson
A1 2
B1 2
End
Tolerance 1e-5
descriptors
End
FOCDFT
End
ExcitonTransfer
Localize OccupiedOnly
fullrun false
End
EndEngine
eor
# In the output one can find the excitonic couplings between the diabetic states.
# The calculated electronic couplings between the 2 singlet excited states
# of A1 symmetry is approximately: 0.15 eV.
# of B1 symmetry is approximately: 0.38 eV.
# The calculated excitonic couplings between the 2 triplet excited states
# of A1 symmetry is approximately: 0.10 eV.
# of B1 symmetry is approximately: 0.027 eV.
# Note that these states may also couple with other higher lying excited states,
# but the most important ones are given above.
# Excition transfer integrals can also be calculated from the energetic splitting
# of excitation energies in the dimer, also called 'Davydov splitting',
# where the effective excitonic coupling equals half the splitting observed.
# This method is used in the final calculation of this example,
# in which a standard CIS calculation is performed on the dimer.
# For convenience the same fragments and symmetry are used as in the previous calculation.
# If one performs the calculation
# the calculated effective excitonic couplings between the 2 lowest singlet excited states
# of A1 symmetry is approximately: 0.15 eV (=0.5*(7.82-7.52)).
# of B1 symmetry is approximately: 0.36 eV (=0.5*(8.20-7.48)).
# The calculated effective excitonic couplings between the 2 lowest triplet excited states
# of A1 symmetry is approximately: 0.10 eV (=0.5*(7.45-7.25)).
# of B1 symmetry is approximately: 0.026 eV (=0.5*(3.556-3.505)).
# In this case the effective excitonic couplings are close to the
# excitonic couplings calculated with FOCDFT. Note that with FOCDFT it is also easy
# to calculate excitonic couplings between diabetic states of different molecules,
# which would be more difficult if one only knows the excitations of the full complex.
AMS_JOBNAME=ET2 $AMSBIN/ams <<eor
System
symmetrize
atoms
C 0.000000 0.000000 0.000000 adf.f=Frag1
C 1.332000 0.000000 0.000000 adf.f=Frag1
H -0.574301 0.000000 -0.928785 adf.f=Frag1
H -0.574301 0.000000 0.928785 adf.f=Frag1
H 1.906301 0.000000 0.928785 adf.f=Frag1
H 1.906301 0.000000 -0.928785 adf.f=Frag1
C -0.000000 4.000000 0.000000 adf.f=Frag2
C 1.332000 4.000000 -0.000000 adf.f=Frag2
H -0.574301 4.000000 0.928785 adf.f=Frag2
H -0.574301 4.000000 -0.928785 adf.f=Frag2
H 1.906301 4.000000 -0.928785 adf.f=Frag2
H 1.906301 4.000000 0.928785 adf.f=Frag2
end
end
Task SinglePoint
Engine ADF
fragments
Frag1 Frag.results/adf.rkf
Frag2 Frag.results/adf.rkf
end
xc
hartreefock
end
TDA
Excitations
Davidson
A1 2
B1 2
End
Tolerance 1e-5
descriptors
End
EndEngine
eor
# As a final example a stacked trimer is calculated, where the distance between
# 2 ethylene molcules is the same as in the dimer.
# In this case only singlet-singlet excitations are calculated,
# where the excited states have B1 symmetry.
# The three lowest localized B1 excitations (diabetic states).
# will be close to the three local B1.u valence excitations on each fragment.
# The calculated excitonic coupling between two neighboring ethylenes will be close to
# that of the dimer, whereas the excitonic coupling bewteen the ethylenes that are furthest
# apart are, as expected, much smaller.
AMS_JOBNAME=ET3_excitontransfer $AMSBIN/ams <<eor
System
symmetrize
atoms
C 0.000000 0.000000 0.000000 adf.f=Frag1
C 1.332000 0.000000 0.000000 adf.f=Frag1
H -0.574301 0.000000 -0.928785 adf.f=Frag1
H -0.574301 0.000000 0.928785 adf.f=Frag1
H 1.906301 0.000000 0.928785 adf.f=Frag1
H 1.906301 0.000000 -0.928785 adf.f=Frag1
C -0.000000 4.000000 0.000000 adf.f=Frag2
C 1.332000 4.000000 -0.000000 adf.f=Frag2
H -0.574301 4.000000 0.928785 adf.f=Frag2
H -0.574301 4.000000 -0.928785 adf.f=Frag2
H 1.906301 4.000000 -0.928785 adf.f=Frag2
H 1.906301 4.000000 0.928785 adf.f=Frag2
C 0.000000 8.000000 0.000000 adf.f=Frag3
C 1.332000 8.000000 0.000000 adf.f=Frag3
H -0.574301 8.000000 -0.928785 adf.f=Frag3
H -0.574301 8.000000 0.928785 adf.f=Frag3
H 1.906301 8.000000 0.928785 adf.f=Frag3
H 1.906301 8.000000 -0.928785 adf.f=Frag3
end
end
Task SinglePoint
Engine ADF
fragments
Frag1 Frag.results/adf.rkf
Frag2 Frag.results/adf.rkf
Frag3 Frag.results/adf.rkf
end
xc
hartreefock
end
TDA
Excitations
onlysing
Davidson
B1 1
End
Tolerance 1e-6
descriptors
End
FOCDFT
End
ExcitonTransfer
Localize OccupiedOnly
fullrun false
End
EndEngine
eor