Correction for dispersion and Coulombic interactions in molecular clusters with density functional derived methods:...

Area of Science:

• Computational Chemistry
• Materials Science

Background:

• Density Functional Theory (DFT) based Tight Binding (DFTB) methods inherit DFT's limitations in describing van der Waals (vdW) interactions.
• Dispersion forces are often poorly represented by standard DFT functionals, necessitating corrections like DFT-D.
• Self-Consistent Charge (SCC) DFTB relies on Mulliken charges, which inaccurately model intermolecular Coulombic potentials.

Purpose of the Study:

• To develop and validate a corrected DFTB (c-DFTB-D) method for improved vdW cluster calculations.
• To address limitations in SCC DFTB's Coulombic potential by incorporating a Class IV/Charge Model 3 (CM3) charge definition.
• To assess the performance of the new c-DFTB-D method against established DFT-D and high-level reference calculations.

Main Methods:

• Implementation of Class IV/CM3 atomic charges within the SCC DFTB framework.
• Derivation of nuclear forces for the modified SCC procedure.
• Application of the c-DFTB-D method to benzene dimer, pyrene dimer, and coronene clusters.
• Comparison with DFT-D, Coupled Cluster (CCSD(T)), and Symmetry Adapted Perturbation Theory (SAPT) calculations.

Main Results:

• The c-DFTB-D method, incorporating improved charge models and dispersion corrections, yields results comparable to DFT-D for benzene dimer.
• Both c-DFTB-D and DFT-D show good agreement with high-accuracy CCSD(T) and SAPT reference calculations.
• For coronene clusters, c-DFTB-D identifies sandwich configurations as more stable than T-shaped ones.

Conclusions:

• The developed c-DFTB-D method offers a more accurate and computationally efficient approach for studying vdW clusters.
• The improved charge model significantly enhances the treatment of intermolecular Coulombic interactions in DFTB.
• This advancement provides a reliable tool for investigating the structure and energetics of polycyclic aromatic hydrocarbon (PAH) clusters.