Improving intermolecular interactions in DFTB3 using extended polarization from chemical-potential equalization.

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Semi-empirical quantum mechanical methods often use minimal basis sets, underestimating molecular polarization and intermolecular interactions, particularly for charged systems.
• Existing methods like DFTB3 struggle with accurate descriptions of non-covalent interactions.

Purpose of the Study:

• To improve the accuracy of the DFTB3 method for calculating intermolecular interaction energies and molecular polarizabilities.
• To develop a more balanced description of various non-covalent interactions, including those involving charged species and dispersion-dominated systems.

Main Methods:

• Augmenting the third-order self-consistent charge density functional tight-binding method (DFTB3) with chemical-potential equalization (CPE) and an empirical dispersion correction (D3).
• Parameterizing the CPE and D3 models using high-level CCSD(T) reference interaction energies and DFT-level dipole moments.
• Considering the impact of molecular polarizabilities in the parameterization process for elements H, C, N, O, and S.

Main Results:

• Significantly reduced Root Mean Square Deviation (RMSD) for interaction energies involving charged species (from 6.07 to 1.49 kcal/mol).
• Improved RMSD for salt bridge interactions (from 5.60 to 1.73 kcal/mol).
• Retained satisfactory performance for dispersion-dominated systems and notably improved polarizabilities of neutral molecules.

Conclusions:

• The augmented DFTB3-D3 method with CPE offers a more accurate and balanced description of diverse non-covalent interactions compared to traditional semi-empirical methods.
• This advancement provides a computationally efficient yet accurate tool for molecular modeling, particularly for systems with charged species.