Basis set dependence of higher-order correlation effects in π-type interactions

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of interaction energies is crucial in chemistry.
• Higher-order correlation effects significantly influence non-covalent interactions.
• Basis set choice critically impacts the accuracy of quantum chemical calculations.

Purpose of the Study:

• To examine the basis set dependence of higher-order correlation effects on π-type interaction energies.
• To evaluate the performance of various basis sets and extrapolation techniques for dimer interaction energies.
• To assess the impact of diffuse functions and counterpoise corrections on calculated energies.

Main Methods:

• Systematic scanning of potential energy surfaces for five π-type dimer systems (acetylene, diacetylene, cyanogen, diphosphorous, 1,4-diphosphabutadiyne).
• Computation of interaction energies using MP2, CCSD, and CCSD(T) methods with 21 basis sets.
• Application of standard extrapolation techniques to obtain complete basis set (CBS) limit energies and correlation corrections.

Main Results:

• Double-ζ basis sets with diffuse functions provided reasonable approximations for δ(CCSD)(CCSD(T)) but struggled with δ(MP2)(CCSD(T)).
• The aug-cc-pVDZ basis set showed minimal deviation from the CBS limit for δ(CCSD)(CCSD(T)) (average 0.06 kcal mol⁻¹).
• Triple-ζ basis sets offered improvements, with aug-cc-pVTZ showing appreciable gains over aug-cc-pVDZ for δ(CCSD)(CCSD(T)). Counterpoise corrections rarely improved results.

Conclusions:

• Basis set choice is critical for accurately describing higher-order correlation effects in π-type interactions.
• Augmented double-ζ basis sets with diffuse functions offer a good balance of accuracy and computational cost for certain correlation effects.
• Complete basis set extrapolation is essential for high-accuracy interaction energy calculations.