2 research outputs found
Universal Exciton Size in Organic Polymers is Determined by Nonlocal Orbital Exchange in Time-Dependent Density Functional Theory
The exciton size
of the lowest singlet excited state in a diverse
set of organic π-conjugated polymers is studied and found to
be a universal, system-independent quantity of approximately 7 Å
in the single-chain picture. With time-dependent density functional
theory (TDDFT), its value as well as the overall description of the
exciton is almost exclusively governed by the amount of nonlocal orbital
exchange. This is traced back to the lack of the Coulomb attraction
between the electron and hole quasiparticles in pure TDDFT, which
is reintroduced only with the admixture of nonlocal orbital exchange
Detailed Wave Function Analysis for Multireference Methods: Implementation in the Molcas Program Package and Applications to Tetracene
High-level
multireference computations on electronically excited
and charged states of tetracene are performed, and the results are
analyzed using an extensive wave function analysis toolbox that has
been newly implemented in the Molcas program package. Aside
from verifying the strong effect of dynamic correlation, this study
reveals an unexpected critical influence of the atomic orbital basis
set. It is shown that different polarized double-ζ basis sets
produce significantly different results for energies, densities, and
overall wave functions, with the best performance obtained for the
atomic natural orbital (ANO) basis set by Pierloot et al. Strikingly,
the ANO basis set not only reproduces the energies but also performs
exceptionally well in terms of describing the diffuseness of the different
states and of their attachment/detachment densities. This study, thus,
not only underlines the fact that diffuse basis functions are needed
for an accurate description of the electronic wave functions but also
shows that, at least for the present example, it is enough to include
them implicitly in the contraction scheme