Is Counterpoise Method a Proper Procedure for Evaluating the Dispersion Energy?

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• The counterpoise (CP) method is standard for correcting basis set superposition error (BSSE) in supermolecular calculations.
• Noncovalent interactions, crucial in molecular systems, are often studied using computational methods that require BSSE correction.

Purpose of the Study:

• To critically examine the effectiveness of the CP method in correcting BSSE for rare gas dimers.
• To investigate the impact of CP correction on potential energy curves at various theoretical levels and basis set sizes.

Main Methods:

• Calculations of potential energy curves for He2, Ne2, and Ar2 dimers.
• Application of CP correction and comparison with uncorrected results.
• Utilized aug-cc-pVxZ basis sets (x=D, T, Q, 5) and theoretical levels (HF, MP2, MP4, CCSD(T)).

Main Results:

• CP correction effectively removes BSSE in Hartree-Fock (HF) energies.
• Applying CP correction to electron correlation energy results in a positive BSSE, leading to shallower potential energy curves.
• The effect is more pronounced with smaller basis sets.

Conclusions:

• The CP method's application to electron correlation energy components requires careful consideration due to potential overcorrection.
• Orbital basis inconsistency (OBI) and configuration basis inconsistency (CBI) explain the contrasting behavior of HF and correlation energy components.
• Findings highlight the need for nuanced application of CP correction in noncovalent interaction studies.