Evaluating dispersion forces for optimization of van der Waals complexes using a non-empirical functional.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Materials science

Background:

• Density functional theory (DFT) struggles to accurately model dispersion interactions.
• Non-empirical dispersion correction models like exchange-dipole moment (XDM) improve DFT accuracy.
• The PW86+PBE+XDM functional offers accurate thermochemistry and van der Waals (vdW) complex properties.

Purpose of the Study:

• To validate the relationship between minimum energy distance and zero force distance for vdW complexes.
• To confirm the reliability of the PW86+PBE+XDM functional for optimizing vdW complexes.
• To assess the impact of computational parameters on accuracy.

Main Methods:

• Utilized the PW86+PBE+XDM functional for DFT calculations.
• Tested 10 rare gas diatomic molecules.
• Employed various integration grids and convergence criteria (10^-6 and 10^-8) in Gaussian09.
• Evaluated forces along the potential energy surface.

Main Results:

• Confirmed that minimum energy distances coincide with zero force distances for vdW complexes.
• Found that convergence criteria (10^-6 or 10^-8) do not impact the accuracy of optimal distances and binding energies.
• Determined that ultra-fine grids are necessary for accurate energies with generalized gradient approximation functionals.

Conclusions:

• The PW86+PBE+XDM functional accurately predicts optimal geometries for vdW complexes by correlating energy minima with force ہاںzero points.
• Computational efficiency can be maintained without sacrificing accuracy by careful selection of convergence criteria.
• Accurate force calculations are essential for optimizing vdW complexes within DFT frameworks.