I am running a RT-TDDFT simulation to study charge transfer between the molecules of a H2 dimer with an extra electron on the bottom H2 molecule. The input file is
title "H2 dimer"
start H2
echo
geometry "mol1" units angstroms noautosym nocenter noautoz
H 0.000 0.000 0.000
H 0.740 0.000 0.000
end
geometry "mol2" units angstroms noautosym nocenter noautoz
H 0.000 0.000 1.800
H 0.740 0.000 1.800
end
geometry "dimer" units angstroms noautosym nocenter noautoz
H 0.000 0.000 0.000
H 0.740 0.000 0.000
H 0.000 0.000 1.800
H 0.740 0.000 1.800
end
BASIS spherical
* library cc-pVDZ
END
set geometry "mol1"
charge -1
dft
odft
mult 2
vectors input atomic output "mol1.movecs"
end
task dft energy
set geometry "mol2"
charge 0
dft
odft
mult 1
vectors input atomic output "mol2.movecs"
end
task dft energy
set geometry "dimer"
charge -1
dft
odft
mult 2
vectors input fragment "mol1.movecs" "mol2.movecs" output "dimer.movecs"
noscf
end
task dft energy
rt_tddft
tmax 200.0
dt 0.2
load vectors "dimer.movecs"
print *
end
task dft rt_tddft
I have tried many basis sets from sto-2g to aug-cc-pVTZ and the results are very different:
H2.png
Shouldn't the results converge as we go to bigger basis sets? If not, how could we be certain that our basis set is the right one for the particular chemical system?
tcne.png
However, i also tried the tetracyanoethylene dimer example on your website with multiple basis sets, and the results are in very good agreement, especially if one considers how different are the basis sets used. So, the question is why in my very simple example above RT-TDDFT fails to produce consistent results with basis set changes? Is there any parameter that could help convergence, or am i totally missing something here?
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