Modifying def2-TZVPP: A Minimal Diffuse Addition for Reliable ΔE Versus ρ(BCP) Relationships in H-Bonded Systems

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Molecular Modeling

Background:

• Basis set quality is crucial for accurate electronic structure calculations, especially for hydrogen-bonded systems.
• The widely used Ahlrichs def2-TZVPP basis set has limitations in describing electron density in low-density intermolecular regions of hydrogen bonds.
• Diffuse flexibility on hydrogen atoms is essential for reliable H-bond region characterization.

Purpose of the Study:

• To develop and validate a minimal, physically motivated extension of the def2-TZVPP basis set for improved hydrogen bond descriptions.
• To enhance the accuracy of electron density calculations in intermolecular regions.
• To provide a more reliable and efficient basis set for Density Functional Theory (DFT) studies of hydrogen-bonded systems.

Main Methods:

• Introduced a minimal extension to def2-TZVPP by adding diffuse p- and d-type polarization functions exclusively to hydrogen atoms.
• Calibrated the exponents of these new functions using Density Functional Theory (DFT) calculations on the ammonia-water complex.
• Targeted the electron density at the bond critical point (BCP) for property-driven optimization.
• Validated the optimized basis set, def2-TZVPP(pol-diff), on a diverse set of biologically relevant molecules with varying H-bond strengths and topologies.

Main Results:

• The optimized def2-TZVPP(pol-diff) basis set accurately reproduces the relationship between interaction energy (ΔEint) and electron density at the BCP (ρ(BCP)).
• The basis set demonstrates good transferability across various inter- and intramolecular hydrogen-bonded systems.
• It improves the description of weak and medium-strength hydrogen bonds and yields reliable electron densities near the BCP.
• Localized diffuse flexibility on hydrogen atoms effectively addresses the limitations of standard basis sets.

Conclusions:

• The def2-TZVPP(pol-diff) basis set offers an efficient and broadly applicable solution for DFT studies of hydrogen-bonded systems.
• This minimal augmentation significantly enhances the description of electron density in crucial intermolecular regions.
• The optimized basis set provides a reliable alternative for accurate molecular modeling of systems with hydrogen bonds.