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

Abstract

We evaluate the impact that the amount of nonlocal Hartree-Fock (%HF) exchange included in a hybrid density functional has on the microscopic parameters (transfer integrals, band gaps, bandwidths, and effective masses) describing charge transport in high-mobility organic crystals. We consider both crystals based on a single molecule, such as pentacene, and crystals based on mixed-stack charge-transfer systems, such as dibenzo-TTF-TCNQ. In the pentacene crystal, the band gap decreases and the effective masses increase linearly with an increase in the amount of %HF exchange. In contrast, in the charge-transfer crystals, while the band gap increases linearly, the effective masses vary only slightly with an increase in %HF exchange. We show that the superexchange nature of the electronic couplings in charge-transfer systems is responsible for this peculiar evolution of the effective masses. We compare the density functional theory results with results obtained within the G 0 W 0 approximation as a way of benchmarking the optimal amount of %HF exchange needed in a given functional.

Microscopic Modeling of Correlated Systems Under Pressure: Representative Examples

“…This can be largely solved by using the range‐separated hybrid functional method of Heyd–Scuseria–Ernzerhof (HSE) where Hartree–Fock corrections to the density functional are introduced. Such corrections have been identified to be important for different kinds of organic systems . It is worth noting that an alternative method, namely GGA + U , is not easily applicable to this organic system, since the bands near the Fermi level have a molecular character and the associated electron density is distributed over many different atoms and orbitals.…”

“…Such corrections have been identified to be important for different kinds of organic systems. [107,[114][115][116] It is worth noting that an alternative method, namely GGA þ U, is not easily applicable to this organic system, since the bands near the Fermi level have a molecular character and the associated electron density is distributed over many different atoms and orbitals. Therefore, the computationally less expensive GGA þ U treatment would require setting the U parameter for all these species, which is a nontrivial task, especially in organic systems.…”

Vibrational properties of organic donor-acceptor molecular crystals: Anthracene-pyromellitic-dianhydride (PMDA) as a case study

“…During the optimization, the positions of the atoms in the unit cell were relaxed, while the cell parameters were kept fixed at the experimental values. Following our earlier study, 20 the impact of HFE has been investigated by using the αPBE functional, based on the original PBE functional, 25,26 following the simple hybrid scheme proposed by Adamo and Barone, 27…”

“…18,19 In order to design new, highly performing CT systems, a deeper understanding of the microscopic parameters that define the electrical and electronic properties of these systems is desirable. In most of the recent studies, the emphasis has been placed on the electronic couplings, 5,9,16,20 while the electron-phonon interactions and vibrational properties of these systems have been much less investigated.…”

“…We found that, whereas in the pentacene crystal, the electronic coupling increases linearly with an increase in HFE, in DBTTF-TCNQ, the electronic couplings for holes and electrons, due to their super-exchange nature, depend only slightly on the HFE amount. 20 Here, we extend this approach to the investigation of the vibrational properties and electron-vibration couplings in CT crystals. The anthracene-PMDA (PMDA = pyromellitic dianhydride) crystal, where anthracene acts as an electron donor (D) and PMDA as an electron acceptor (A), is taken as a representative system ( Fig.…”