Tuned range separated hybrid functionals for solvated low bandgap oligomers.

Area of Science:

• Computational Chemistry
• Theoretical Chemistry
• Materials Science

Background:

• Time-dependent density functional theory (TDDFT) struggles with charge transfer excitations.
• Optimally tuned range-separated hybrid (OT-RSH) functionals offer improved accuracy for charge transfer excitations.
• Describing solvated or embedded systems with OT-RSH functionals remains a significant challenge.

Purpose of the Study:

• To develop and demonstrate a method for accurately describing charge transfer excitations in solvated systems using OT-RSH functionals.
• To investigate the calculation of ionization energies and optical gaps for solvated oligothiophenes.
• To elucidate the ambiguities in parameter tuning for OT-RSH functionals in solution.

Main Methods:

• Utilizing locally projected self-consistent field (SCF) diagonalization on an absolutely localized molecular orbital (ALMO) expansion.
• Explicitly representing dioxane solvent molecules in calculations.
• Gradually extending the solvated system to obtain a consistent estimate of the optimal range-separated parameter (ω) at the bulk solvation limit.

Main Results:

• The proposed method successfully determines ionization energies and optical gaps of solvated oligothiophenes.
• The optimal range-separated parameter (ω) is influenced by solvent molecules beyond the first coordination sphere.
• Accurate optical gap calculations require considering the chemical environment for parameter determination, solvent screening, and realistic geometries.

Conclusions:

• A robust computational approach is established for accurately calculating optical gaps of solvated systems using OT-RSH functionals.
• The findings provide a pathway to overcome computational and conceptual challenges in applying OT-RSH functionals to complex systems.
• This work is relevant for advancing organic electronics through improved theoretical modeling.