Theoretical Study of the Local and Charge-Transfer Excitations in Model Complexes of Pentacene-C₆₀ Using Tuned Range-Separated Hybrid Functionals

Abstract

The characteristics of the electronic excited states and the charge-transfer processes at organic-organic interfaces play an important role in organic electronic devices. However, charge-transfer excitations have proven challenging to describe with conventional density functional theory (DFT) methodologies due to the local nature of the exchange-correlation potentials often employed. Here, we examine the excited states of model pentacene-C60 complexes using time-dependent DFT with, on one hand, one of the most popular standard hybrid functionals (B3LYP) and, on the other hand, several long-range corrected hybrid functionals for which we consider both default and nonempirically tuned range-separation parameters. The DFT results based on the tuned functionals are found to agree well with the available experimental data. The results also underline that the interface geometry of the complex has a strong effect on the energies and ordering of the singlet and triplet charge-transfer states.

Impact of exact exchange in the description of the electronic structure of organic charge-transfer molecular crystals

“…It has been suggested recently that an improved description of chargetransfer states can be obtained by employing range-separated hybrid functionals, especially those with system-tuned rangeseparation parameters [38]. While there are now multiple examples of applying these functionals to the donor-acceptor complexes [39,40], their application to donor-acceptor crystals is still missing. Such investigations in our group are now underway, and the related results will be reported elsewhere.…”

Ionization Energies, Electron Affinities, and Polarization Energies of Organic Molecular Crystals: Quantitative Estimations from a Polarizable Continuum Model (PCM)-Tuned Range-Separated Density Functional Approach

“…Due to the absence of a GW value for TIPS-pentacene, we approximated the dielectric constant by using the same ε = 3.6 as for pentacene 17 ; similarly, for PC 60 BM, C 70 , and P C 70 BM, we used the same ε = 5.0 as for C 60 . 17 Where available, we also provide the experimental ε values.…”

“…While all these molecules have been studied before using optimal tuning methods in the gas phase, 37,48,70 we report here the results obtained from the PCM-tuning of their respective organic crystals. The basic idea is to employ the PCM model using the magnitudeequivalent dielectric constant (ε) of the crystal to simulate the crystal environment during the IPtuning process.…”

Can Gap Tuning Schemes of Long-Range Corrected Hybrid Functionals Improve the Description of Hyperpolarizabilities?

“…[45][46][47][48][51][52][53] Thus, one could expect more accurate hyperpolarizability predictions from tuned LC-DFT functionals as compared to their unoptimized counterparts.…”