Exploring non-covalent interactions in excited states: beyond aromatic excimer models

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Time-dependent density functional theory (TD-DFT) is a cost-effective method for excited state calculations.
• Conventional TD-DFT struggles with accurately describing non-covalent interactions (NCIs), similar to ground-state DFT.
• Accurate modeling of excited-state NCIs is crucial for understanding exciplex behavior.

Purpose of the Study:

• To benchmark various TD-DFT methods for their accuracy in describing excited-state non-covalent interactions (NCIs) in exciplexes.
• To evaluate the impact of ground-state dispersion corrections (DFT-D3(BJ), VV10) on TD-DFT calculations of exciplex binding energies.
• To identify the most reliable TD-DFT approaches for modeling exciplexes across different excitation types and geometries.

Main Methods:

• Calculation of dissociation curves for model exciplexes to assess binding strengths.
• Benchmarking TD-DFT methods against high-level wave function calculations (SCS-CC2/CBS(3,4)).
• Inclusion and evaluation of DFT-D3(BJ) and VV10 dispersion corrections in TD-DFT calculations.

Main Results:

• TD-DFT methods generally underbind exciplexes, primarily due to the omission of dispersion forces.
• Dispersion corrections, particularly DFT-D3(BJ), are essential for achieving good accuracy in exciplex binding energies.
• VV10-type non-local kernels show promise but primarily affect ground-state energies; double hybrid functionals (B2GP-PLYP-D3(BJ), B2PLYP-D3(BJ)) are robust for localized excitations.

Conclusions:

• Ground-state dispersion corrections are vital for accurate TD-DFT description of exciplex binding.
• Double hybrid functionals with dispersion corrections offer reliable performance for exciplexes with localized excitations.
• Future improvements require addressing the need for state-specific dispersion corrections in TD-DFT.