Quantifying Intramolecular Basis Set Superposition Errors.

Area of Science:

• Computational chemistry
• Quantum chemistry
• Molecular modeling

Background:

• Basis set superposition error (BSSE) is a known artifact in quantum chemical calculations.
• Accurate conformational analysis is crucial for understanding molecular properties and interactions.

Purpose of the Study:

• To quantify intramolecular basis set superposition errors (BSSE) in medium-sized Gaussian basis sets.
• To evaluate methods for mitigating BSSE in large molecular systems.
• To assess the impact of BSSE on conformational preferences.

Main Methods:

• Hartree-Fock (HF) and Density Functional Theory (DFT) calculations were performed.
• Calculations utilized medium-sized Gaussian basis sets (e.g., polarized double zeta, polarized triple zeta).
• Intramolecular BSSE was investigated for a 186-atom decapeptide.
• Two BSSE correction procedures and multiresolution methods based on Multiwavelets were tested.

Main Results:

• Significant intramolecular BSSE (up to ~80 kJ/mol) was observed with polarized double zeta basis sets.
• Errors were reduced to ~10 kJ/mol with polarized triple zeta basis sets.
• Larger basis sets (polarized quadruple zeta) or multiresolution methods were required to minimize BSSE below a few kJ/mol.
• BSSE artificially stabilized compact conformations over extended ones.

Conclusions:

• Medium-sized Gaussian basis sets introduce substantial intramolecular BSSE, impacting conformational stability.
• Accurate conformational prediction necessitates larger basis sets or advanced techniques like multiresolution methods.
• BSSE must be carefully addressed for reliable computational studies of large molecules.