Improved Prediction of Properties of π-Conjugated Oligomers with Range-Separated Hybrid Density Functionals

Abstract

Range-separated hybrid functionals along with global hybrids and pure density functionals have been employed to calculate geometries, ionization energies (IP)s, electron affinities (EA)s, and excitation energies of neutral and oxidized polyenes, thiophene, and furan oligomers. Long-range correction with 100% HF exchange solves the problem of density functional theory with incorrect chain length dependence of IPs and energy gaps. There is a possibility of overcorrection, if the short-range part of the functional with no or low HF exchange is too small. The wB97XD functional with 22% of HF exchange in the short-range and a range-separation parameter of 0.2 seems to be just right for conjugated systems at all chain lengths. The wB97XD functional additionally produces negative orbital energies in very good agreement with IPs and EAs. With correct orbital energies, band gaps correspond to transport gaps (Et) and not to optical gaps (Eg). Et is much larger than Eg in the gas phase, but the difference is significantly smaller in the solid state. The accuracy of the negative orbital energies is good down to about 30 eV so that valence and innervalence PE spectra can be modeled. wB97XD is therefore suitable for calculating band structures of conjugated polymers employing orbital energies.

Induction and control of supramolecular chirality by light in self-assembled helical nanostructures

“…The long-range corrected hybrid density functional with damped atom-atom dispersion correction, oB97X-D, was used 52 . This functional can handle p-p interaction empirically and have been successfully used to model polymer structures with large number of atoms [53][54][55] . The 6-31G* basis set was used to describe atomic orbitals.…”

Length dependence of ionization potentials of transacetylenes: Internally consistent DFT/GWapproach

“…(1), IP SCF , is usually more accurate than that from the plain HOMO energy − N N because it is less affected by the self-interaction error [24]. However, going from short oligomers to more extended systems, different DFT functionals give rise to a different length dependence of the IP SCF , ranging from concave and straight to convex as a function of inverse length [25], so the problem is still under discussion.…”

Trends in molecular design strategies for ambient stable n-channel organic field effect transistors

“…[112][113][114][115][116][117][118] There is not much difference between the predictions with different correlation functionals as the most important parameter for determining the properties of conjugated systems is the amount of Hartree-Fock (HF) exchange. Increasing the amount of HF-exchange decreases defect sizes, increases spincontamination, 119 122 and the direct coupling method. 123 The simplest of the three, the energy-splitting-in-dimer method, however, tends to underestimate t. 124 As mobilities increase with increasing t and decreasing l while both increase with HF-exchange, it is possible to manipulate the predicted mobilities by calculating l and t with different density functionals.…”