R^-8 Dispersion Interaction: Derivation and Application to the Effective Fragment Potential Method

Area of Science:

• Computational chemistry
• Quantum chemistry
• Molecular modeling

Background:

• Accurate calculation of dispersion forces is crucial for molecular simulations.
• The effective fragment potential (EFP) method offers a computationally efficient approach to model intermolecular interactions.
• Existing EFP models require refinement for precise description of dispersion energy contributions.

Purpose of the Study:

• To derive and implement anisotropic and isotropic R^-8 dispersion (disp8) contributions within the EFP framework.
• To extend damping functions for disp8 and implement analytic gradients for the isotropic component.
• To evaluate the accuracy of the new EFP disp8 model against symmetry-adapted perturbation theory (SAPT) benchmarks.

Main Methods:

• Formulation of EFP with imaginary frequency-dependent Cartesian polarizability tensors.
• Distribution of polarizability tensors at localized molecular orbital (LMO) centroids.
• Derivation and implementation of origin-shifting transformations for polarizability tensors.
• Development of analytic gradients for isotropic disp8.
• Extension of intermolecular overlap-based and Tang-Toennies damping functions.

Main Results:

• Isotropic disp8 improves agreement with SAPT benchmarks, reducing mean absolute errors (MAEs).
• Anisotropic disp8 enhances accuracy but can overbind at short ranges (overlap > 0.1).
• The new EFP dispersion model with isotropic disp8 shows good curvature and agreement with SAPT around equilibrium.
• Overlap-based damping functions outperform Tang-Toennies but still require improvement for short-range screening.

Conclusions:

• The developed EFP disp8 model, particularly the isotropic component, offers a significant improvement in calculating dispersion energies.
• Further development is needed to address the overestimation of dispersion interactions at short ranges for both isotropic and anisotropic components.
• The study provides a more accurate and refined approach for modeling dispersion forces in molecular systems using the EFP method.