Can the Counterpoise Correction for Basis Set Superposition Effect Be Justified?

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• The basis set superposition effect (BSSE) is a widely accepted phenomenon in quantum chemistry.
• The counterpoise method is the standard approach to correct for BSSE.
• The underlying assumption is that basis sets are biased towards dimers.

Purpose of the Study:

• To test the validity of the counterpoise correction method for BSSE.
• To investigate the bias of standard quantum chemistry basis sets on monomer and dimer calculations.
• To determine if the counterpoise correction improves accuracy compared to basis set limit values.

Main Methods:

• Calculations were performed on small systems, specifically Be2, for which basis set limit benchmarks are available.
• Basis set errors for monomers and dimers were analyzed at both Hartree-Fock and correlated levels (CCSD(T), Full CI).
• The impact of the counterpoise correction on calculated bond energies was evaluated against benchmark data.

Main Results:

• Standard basis sets in quantum chemistry exhibit a bias towards atoms, with larger basis set errors for dimers than monomers.
• The counterpoise correction amplifies this imbalance by further reducing the monomer's basis set error.
• Counterpoise-corrected bond energies showed greater deviation from basis set limit values compared to uncorrected energies.

Conclusions:

• The hypothesis that basis sets are biased towards dimers is incorrect; they appear biased towards atoms.
• The counterpoise correction method can lead to less accurate results by increasing the deviation from true basis set limit values.
• The findings challenge the universal applicability and accuracy of the standard counterpoise correction for BSSE.