An Efficient a Posteriori Treatment for Dispersion Interaction in Density-Functional-Based Tight Binding.

Area of Science:

• Computational Chemistry
• Materials Science

Background:

• Accurate modeling of intermolecular forces like London dispersion is crucial in computational chemistry.
• Standard Density Functional Theory (DFT) methods often fail to adequately describe van der Waals interactions, particularly in systems involving hydrogen molecules and polycyclic aromatic hydrocarbons (H2/PAH).

Purpose of the Study:

• To evaluate the performance of various quantum chemical methods, including DFT, DFTB, and ab initio approaches, in capturing London dispersion forces.
• To propose and validate an improved computational approach for H2/PAH interactions.

Main Methods:

• Investigated DFT functionals (VWN-LDA, PBE-GGA, B3LYP), DFTB, and ab initio methods (HF, MP2, CCSD, CCSD(T)).
• Developed and tested an a posteriori van der Waals correction for DFTB.
• Compared results with experimental data for bulk graphite properties.

Main Results:

• DFT methods showed inadequacy in describing H2/PAH interactions due to poor treatment of London dispersion.
• The proposed DFTB method with an added van der Waals term yielded results comparable to high-level ab initio calculations (MP2, CCSD(T)).
• The enhanced DFTB method also accurately reproduced bulk properties of graphite.

Conclusions:

• Standard DFT functionals are insufficient for accurate H2/PAH interaction modeling.
• The modified DFTB approach offers a computationally efficient and accurate alternative for studying van der Waals forces in such systems.
• This method shows promise for materials science applications involving PAHs and gas adsorption.