Infinite Basis set extrapolation for Double Hybrid Density Functional Theory 1: effect of applying various...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of molecular properties is crucial for understanding chemical phenomena.
• Density Functional Theory (DFT) methods, particularly Double Hybrid DFT (DHDF), offer a balance of accuracy and efficiency.
• Extrapolation techniques are employed to estimate properties at the Complete Basis Set (CBS) limit.

Purpose of the Study:

• To evaluate the efficacy of the Infinite Basis (IB) set extrapolation method when combined with DHDF.
• To assess the accuracy of various extrapolation functions for determining molecular properties.
• To determine the optimal basis set size for achieving chemical accuracy.

Main Methods:

• Application of IB set extrapolation and DHDF to calculate various molecular energy databases.
• Estimation of CBS limit using extrapolation functions (exponential, inverse power, modified exponential).
• Comparison of results obtained with different basis sets (e.g., cc-pVDZ, cc-pVTZ, cc-pV[T|Q]Z).

Main Results:

• The B2KPLYP/cc-pV[D|T]Z combination yielded results of quadruple-ζ quality.
• Achieving ~2 kcal/mol chemical accuracy necessitated the use of cc-pV[T|Q]Z basis sets.
• Extrapolation with two basis sets proved satisfactory, with minor variations across different extrapolation functions.

Conclusions:

• The DHDF-IB scheme is a robust method for calculating molecular properties.
• The choice of basis set significantly impacts the achievable chemical accuracy.
• Further improvements can be expected by incorporating diffuse basis functions into the DHDF-IB scheme.