Screened optimally tuned range separated hybrid functional for solvated low bandgap molecular systems

Area of Science:

• Computational Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Density functional theory (DFT) and time-dependent DFT (TD-DFT) with optimally tuned range-separated hybrid (OT-RSH) functionals are crucial for predicting molecular electronic properties, especially charge transfer excitations.
• The system-dependent range-separating parameter (ω) in OT-RSH functionals presents optimization challenges, particularly concerning the influence of the chemical environment.
• Previous work showed gap renormalization in molecular crystals can be modeled using OT-RSH functionals screened by the static dielectric constant (ɛstatic).

Purpose of the Study:

• To propose and validate a new OT-RSH functional screened by the high-frequency dielectric constant (ɛ∞), termed OT-sRSH, for calculating electronic properties in dielectric environments.
• To assess the accuracy of the OT-sRSH functional for vertical ionization energies and optical gaps of S,N-heteroacene derivatives in solution.
• To compare the performance of OT-sRSH with explicitly solvated OT-RSH calculations for various molecular systems.

Main Methods:

• Implementation and application of the OT-sRSH functional for electronic structure calculations.
• Computational modeling of S,N-heteroacene derivatives in tetrahydrofuran and dichloromethane.
• Comparison of OT-sRSH results with experimental ionization potentials (IPs) and optical gaps (Egs).
• Comparative analysis against explicitly solvated OT-RSH calculations for oligothiophenes, benzene, and methylene blue.

Main Results:

• The standard OT-RSH functional underestimated experimental IPs and Egs by up to 1.5 eV and 0.5 eV, respectively.
• The proposed OT-sRSH functional significantly improved accuracy, underestimating IPs and Egs by only 0.4 eV and 0.2 eV.
• OT-sRSH and explicitly solvated OT-RSH methods showed similar performance for weakly interacting systems but diverged for strongly interacting solute-solvent systems.

Conclusions:

• The OT-sRSH functional effectively incorporates environmental polarization effects, offering an accurate and computationally efficient approach for studying molecular systems.
• This method represents a significant advancement towards the reliable computational description of realistic molecular systems, including their interactions with the surrounding environment.
• The OT-sRSH functional provides a valuable tool for predicting electronic properties where solvent effects are significant.