Validation of dispersion-corrected density functional theory approaches for ionic liquid systems

Area of Science:

• Computational Chemistry
• Materials Science
• Physical Chemistry

Background:

• Accurate theoretical modeling of ionic liquids is crucial for understanding their properties.
• Standard density functional theory (DFT) methods often neglect crucial dispersion interactions.
• Møller-Plesset perturbation theory (MP2) serves as a benchmark for evaluating DFT performance.

Purpose of the Study:

• To evaluate the performance of various DFT functionals for ionic liquid systems.
• To assess the impact of dispersion correction schemes on DFT accuracy.
• To compare DFT results with high-level Møller-Plesset perturbation theory calculations.

Main Methods:

• Systematic testing of generalized gradient approximation (GGA), meta-GGA, and hybrid DFT functionals.
• Inclusion of two dispersion correction methods: 1/r(6) term and dispersion-corrected atom-centered potentials.
• Validation against Møller-Plesset perturbation theory (MP2) for structural and energetic properties.

Main Results:

• Neglecting dispersion leads to inaccurate structural stability trends for the 1-butyl-3-methylimidazolium cation.
• Dispersion-corrected DFT methods dramatically improve agreement with MP2, reducing mean absolute deviation (MAD) to < 10 kJ/mol for energies.
• Hartree-Fock and standard DFT methods show large MADs (up to 178 pm) for intermolecular distances, while dispersion-corrected methods achieve MAD < 50 pm.

Conclusions:

• Dispersion interactions are essential for accurate theoretical descriptions of ionic liquids.
• Dispersion-corrected DFT approaches provide a significant improvement over standard DFT and Hartree-Fock methods.
• These improved methods are vital for reliable predictions of ionic liquid structures and energetics.