How does basis set superposition error change the potential surfaces for hydrogen-bonded dimers?

TLDR

The study introduces a method to automate geometry optimization of supermolecule calculations on potential surfaces corrected for basis set superposition error using the counterpoise technique. The method was applied to HF/HCN, HF/H₂O, and HCCH/H₂O complexes with 6‑31G(d,p) and D95++(d,p) basis sets at Hartree–Fock and MP2 levels, producing interaction energies, geometries, and vibrational frequencies on CP‑optimized surfaces and comparing them to conventional single‑point CP corrections. Optimization on CP‑corrected surfaces produces more negative interaction energies (before vibrational corrections) and lower H‑bond stretching frequencies, with effect magnitudes ranging from very small to quite large and not predictable from the stretching frequencies alone.

Abstract

We describe a simple method to automate the geometric optimization of molecular orbital calculations of supermolecules on potential surfaces that are corrected for basis set superposition error using the counterpoise (CP) method. This method is applied to the H-bonding complexes HF/HCN, HF/H2O, and HCCH/H2O using the 6-31G(d,p) and D95++(d,p) basis sets at both the Hartree–Fock and second-order Mo/ller–Plesset levels. We report the interaction energies, geometries, and vibrational frequencies of these complexes on the CP-optimized surfaces; and compare them with similar values calculated using traditional methods, including the (more traditional) single point CP correction. Upon optimization on the CP-corrected surface, the interaction energies become more negative (before vibrational corrections) and the H-bonding stretching vibrations decrease in all cases. The extent of the effects vary from extremely small to quite large depending on the complex and the calculational method. The relative magnitudes of the vibrational corrections cannot be predicted from the H-bond stretching frequencies alone.