Exchange-Correlation Effects for Noncovalent Interactions in Density Functional Theory.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Density-functional theory (DFT) is widely used for electronic structure calculations.
• Accurate modeling of noncovalent interactions is crucial for understanding molecular systems.
• Dispersion-corrected DFT methods aim to improve the description of van der Waals forces.

Purpose of the Study:

• To analyze the impact of exchange-correlation functional errors on noncovalent interactions.
• To benchmark different density-functional approximations using a molecular many-body expansion.
• To identify and characterize the sources of error in DFT modeling of intermolecular forces.

Main Methods:

• Computed CCSD(T) reference binding energies for small-molecule clusters.
• Decomposition of binding energies using a molecular many-body expansion.
• Benchmarking of density-functional approximations, including semilocal functionals, exact-exchange admixture, and range separation.

Main Results:

• Three primary error sources identified: repulsion, delocalization, and deformation errors.
• Repulsion error stems from semilocal functional approximations and affects intermolecular repulsions.
• Delocalization error depends on exact exchange and impacts induction and electrostatic energies; deformation error affects monomer relaxation.

Conclusions:

• Many-body errors from exchange-correlation functionals often exceed dispersion correction magnitudes.
• Accurate noncovalent interaction modeling requires dispersion corrections and careful functional design to minimize repulsion and delocalization errors.
• Future functionals must balance semilocal components, exact exchange, and correlation to achieve high accuracy.