Fundamental Gaps of Condensed-Phase Organic Semiconductors from Single-Molecule Calculations using Polarization-Consistent Optimally Tuned Screened Range-Separated Hybrid Functionals

Abstract

Range-separated hybrid (RSH) functionals have been shown to overcome the tendency of traditional density functional theory to underestimate the fundamental orbital gap. More recently, the screened RSH (SRSH) approach has been developed as a means to extend these functionals to address the effect of the electrostatic environment on the fundamental gap. Here, we report a scheme that combines the SRSH formulation with the polarized continuum model (PCM) within a consistent framework for addressing long-range screened electrostatic interactions, which is further improved by optimal tuning (OT). The quantitative predictive power of the new OT-SRSH-PCM scheme is demonstrated by addressing fundamental gaps in thin films of organic semiconducting materials. This is especially impressive as the approach is based on single molecule calculations. We also discuss the advantages of this approach over alternative schemes combining PCM with RSH. In particular, we show that it avoids the well-documented tendency of standard OT to collapse the range separation parameter when performed within a dielectric continuum.

Efficient Charge Generation via Hole Transfer in Dilute Organic Donor–Fullerene Blends

“…Additional calculations are performed for single molecules and their ions. Condensed phase effects are addressed by the SRSH-PCM framework (16,18). All ground state optimizations and normal mode calculations are carried out employing density functional theory (DFT) at ωB97X-D/6-31G* level (33,34) within the conductor-like polarizable continuum model (PCM) (35).…”

“…Importantly the SRSH-PCM framework achieves a polarization-consistent treatment of the molecular electronic structure affected by the condensed environment represented through the dielectric constant. (16) The range separation parameter (γ) is tuned following the J2(γ) scheme (37), and is found to be 0.180 bohr -1 for C70 and 0.110 bohr -1 for DBP and the dyad, where alpha is set to 0.2 and beta is reset according to the dielectric constant. The electronic coupling between pairs of dyad states are calculated using the fragment-charge difference method (FCD) (38), where the DBP acts as donor and the C70 as acceptor region.…”

“…As energy and charge transfer processes strongly depend on the excitation energies, we employ the polarizationconsistent SRSH-PCM framework, which has been shown to yield accurate excitation energies for both excitonic and CT states of condensed phase molecular systems. (16,18). Our analysis considers a DBP-C70 complex in its optimized geometry, assuming that delocalization effects become relevant only on later timescales.…”

“…In this context, long-range interactions and polarization effects must be accounted for to achieve a reliable description of interfacial CT states (15). In this study, we employ an approach based on screened range-separated hybrid functionals (SRSH) recently shown to accurately address condensed phase effects on ground state transport properties (16) and excited state properties of solvated pigments. (17,18) The polarization consistent approach invokes SRSH within a polarized continuum model (PCM) in TDDFT calculations of the excited states.…”

Synergistic Approach of Ultrafast Spectroscopy and Molecular Simulations in the Characterization of Intramolecular Charge Transfer in Push-Pull Molecules

“…Range Separated Hybrid (RSH) functionals were proposed to predict with good accuracy the energetics of charge transfer states [70][71][72][73][74], achieving an agreement with experiments when combined with Polarized Continuum Models (PCM) [75]. Furthermore, the combination of Screened-Range Separated Hybrid (SRSH) functional with PCM [76][77][78] allows to predict CT states in condensed phases that accounts effectively for the electrostatic environment. In particular, the energetics of the weakly interacting D-A complexes of pentacene with C60 and poly-3-hexylthiophene (P3HT) calculated within the SRSH-PCM framework, was disclosed to well agree with the experimental energies in the condensed phase [77].…”