Evaluation of alkali metal cation affinities and basicities using extrapolation to the complete basis set limit

Area of Science:

• Computational Chemistry
• Quantum Chemistry

Background:

• Accurate prediction of molecular properties is crucial in chemistry.
• Complete basis set (CBS) extrapolation is a widely used technique to approximate results at the limit of an infinitely large basis set.

Purpose of the Study:

• To develop and validate robust and well-calibrated CBS extrapolation methods for Hartree-Fock (HF) and second-order Møller-Plesset (MP2) perturbation theory.
• To determine the optimal CBS scheme for calculating alkali metal cation affinities and basicities.

Main Methods:

• Employed CBS extrapolation at HF and MP2 levels using the def2-xZVP basis set series (x = 2-4).
• Investigated separate extrapolation of HF and correlation energies.
• Proposed a specific CBS scheme: E(CBS)[∞] = 1.10529·E(HF)[4] - 0.10529·E(HF)[2] + 0.92703·E(CE)[4] - 0.07297·E(CE)[2].
• Highlighted the need for adjusted parameters for heavier elements (third row and beyond).

Main Results:

• The developed CBS methods demonstrate high accuracy, with absolute deviations between theoretical and experimental data often smaller than experimental uncertainties.
• Separate extrapolation of HF and correlation energies proved particularly effective.
• The proposed CBS scheme provides excellent results for alkali metal cation affinities and basicities.

Conclusions:

• CBS extrapolation, particularly when HF and correlation energies are treated separately, offers a general, robust, and well-calibrated approach for high-accuracy quantum chemical calculations.
• The study provides a refined CBS scheme for predicting alkali metal cation affinities and basicities.
• Consideration of basis set parameters is essential for calculations involving heavier elements.