Does Basis Set Superposition Error Significantly Affect Post-CCSD(T) Corrections?

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Coupled cluster theory, particularly CCSD(T), is a high-accuracy method for electronic structure calculations.
• Basis set superposition error (BSSE) can affect the accuracy of calculated interaction energies and atomization energies.
• Counterpoise corrections are commonly used to mitigate BSSE.

Purpose of the Study:

• To investigate the impact of counterpoise corrections on post-CCSD(T) contributions in both atomization energy and noncovalent interaction benchmarks.
• To assess the significance of BSSE for different levels of theory and basis sets.

Main Methods:

• Evaluation of counterpoise corrections for post-CCSD(T) energy contributions.
• Analysis of BSSE on W4-11 total atomization energies benchmark.
• Analysis of BSSE on A24x8 noncovalent interactions benchmark.
• Utilizing various basis sets, including cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ.

Main Results:

• Counterpoise corrections to post-CCSD(T) contributions are generally two orders of magnitude smaller than to the CCSD(T) interaction energy.
• BSSE on connected quadruple substitutions (Q) and higher-order excitations are negligible.
• For atomization energies, BSSE can be noticeable with small basis sets (e.g., cc-pVDZ) but becomes insignificant with larger basis sets and extrapolation methods (W4, HEAT).
• In noncovalent dimers, differential BSSE on post-CCSD(T) correlation is negligible even with small basis sets.

Conclusions:

• Counterpoise corrections are of minor importance for post-CCSD(T) correlation contributions in noncovalent interactions.
• The impact of BSSE on atomization energies is effectively removed by standard high-level thermochemistry protocols.
• The study highlights the diminishing role of BSSE at higher levels of theory and with larger basis sets.