Calculating Off-Site Excitations
in Symmetric Donor–Acceptor
Systems via Time-Dependent Density Functional Theory with Range-Separated
Density Functionals
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Abstract
Time-dependent density functional theory with range-separated
hybrid
functionals is used to calculate off-site excitations involving transitions
between spatially separated orbitals in weakly coupled systems. Although
such off-site excitations involve charge transfer, orbital degeneracy
in symmetrical systems results in linear combinations of off-site
excitations with equal weights and therefore zero net charge-transfer
character. Like other types of off-site excitations, such “hidden”
charge-transfer excitations are not accurately captured by conventional
density functionals. We show that the recently introduced Baer–Neuhauser–Livshitz
range-separated hybrid functional accurately characterizes such hidden
off-site excitation energies via applications to the ethene dimer
model system and to dye-functionalized silsesquioxanes