Van der Waals Interactions in Density-Functional Theory: Rare-Gas Diatomics

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Conventional generalized gradient approximation (GGA) and meta-GGA density functionals struggle to accurately describe van der Waals (vdW) interactions.
• These functionals often lack the necessary physics for dispersion interactions, leading to significant overbinding or over-repulsion issues.
• The exchange component alone can drastically affect interaction energies depending on the functional chosen.

Purpose of the Study:

• To evaluate various exchange GGAs for their ability to replicate exact Hartree-Fock repulsion energies in rare-gas systems.
• To develop an improved density functional theory (DFT) approach for vdW interactions.
• To achieve accurate interaction curves for rare-gas pairs using a computationally efficient method.

Main Methods:

• Assessment of diverse exchange GGAs against exact Hartree-Fock repulsion energies for rare gases.
• Incorporation of a dynamical correlation GGA and the nonempirical dispersion model by Becke and Johnson.
• Development of a GGA plus dispersion theory using the PW86 exchange functional.

Main Results:

• The PW86 exchange functional demonstrated remarkable performance in reproducing Hartree-Fock repulsion energies.
• The developed GGA plus dispersion theory yielded excellent interaction curves for rare-gas pairs (He through Kr).
• The model requires only two adjustable parameters for dispersion term damping, indicating high efficiency.

Conclusions:

• The PW86 functional is a strong candidate for describing exchange interactions in vdW systems.
• The proposed GGA plus dispersion theory offers a robust and accurate method for calculating rare-gas interactions.
• This approach provides a significant improvement over conventional DFT functionals for dispersion-bound systems.