Below is an example for calculating the excited state response with RT-TDDFT for the 5th excited state of a water molecule. Some items to note:
-A LR-TDDFT gradient calculation needs to be performed first in order to generate the excited state density matrix
-That density matrix needs to be loaded within the RT-TDDFT block of the input
-In addition to the RT-TDDFT runs with field applied (here I have only done the excitation along the x-axis), an additional run needs to be done without any field applied; this extra run is used to correct the dipole moments from the runs with an applied field
Obtaining transition densities to plot is significantly more involved than just the spectrum. You need to add a visualization block to each RT-TDDFT input block. This will generate a density matrix file for each step in each RT-TDDFT run. Then as with the dipole moment, the run without a field is used to correct the runs with a field. In the examples that we showed in the paper, the probed transitions were polarized along a single axis so we just used the density matrices from the run with a field along that axis. After a series of corrected density matrices are generated, then you need to take the Fourier transform of the density matrices at the transition frequency. The resulting density matrix can then be fed into DPLOT to generate a cube file for visualization.
echo
start water
geometry "system" units angstroms nocenter noautoz noautosym
O 0.00000000 0.00000000 0.15104872
H -0.75808206 0.00000000 -0.48477224
H 0.75808206 0.00000000 -0.48477224
end
set geometry "system"
basis
* library STO-3G
end
dft
xc hfexch 1.0
end
tddft
nroots 10
notriplet
civecs
grad
root 5
end
end
task tddft gradient
unset rt_tddft:*
rt_tddft
tmax 200.0
dt 0.2
load density water.dmat
tag "ref"
print dipole
end
task dft rt_tddft
unset rt_tddft:*
rt_tddft
tmax 200.0
dt 0.2
load density water.dmat
tag "kick_x"
print dipole
field "kick"
type delta
polarization x
max 0.0001
end
excite "system" with "kick"
end
task dft rt_tddft
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