Validation of density functionals for pancake-bonded π-dimers; dispersion is not enough

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• π-Stacking pancake bonding in radical systems presents unique challenges for computational chemistry.
• These interactions involve short contact distances, multireference character, and significant dispersion forces, complicating theoretical modeling.

Purpose of the Study:

• To evaluate the performance of over 50 density functional theories (DFTs) for modeling π-stacking pancake bonding.
• To identify accurate DFT methods for specific radical π-dimer systems.

Main Methods:

• Tested more than 50 DFTs, including 22 with dispersion corrections.
• Evaluated energetic and geometric parameters against high-level multireference average quadratic coupled cluster (MR-AQCC) benchmarks.
• Focused on four distinct π-dimerized pancake-bonded systems.

Main Results:

• No single DFT excelled across all tested pancake-bonded systems.
• M05-2X and PBE0-MBD were accurate for the phenalenyl π-dimer.
• BLYP was the best choice for the 1,2,4,6-thiatriazine π-dimer.
• O3LYP performed best for the 1,3,2,4,6-dithiatriazine π-dimer, and MN15L for K+TCNE-.

Conclusions:

• The study highlights the system-specific nature of DFT performance in modeling radical π-stacking.
• Findings offer guidance for selecting appropriate DFTs in the design and characterization of pancake-bond based materials.
• Results can inform the development of improved DFT functionals for such challenging interactions.