Further analysis and comparative study of intermolecular interactions using dimers from the S22 database

Area of Science:

• Computational chemistry
• Quantum chemistry

Background:

• Accurate calculation of molecular interaction energies is crucial for understanding non-covalent interactions.
• Developing reliable density functional theory (DFT) and force field models requires high-quality reference data.

Purpose of the Study:

• To compute accurate interaction energy curves for molecular dimers using MP2 and CCSD(T) methods.
• To investigate the impact of basis set superposition error (BSSE) on interaction energy calculations.
• To provide reference data for developing improved DFT and force field models.

Main Methods:

• Complete basis set (CBS) extrapolation using MP2 and CCSD(T) methods.
• Fitting analytical Morse curves to the computed interaction energies.
• Analysis of basis set superposition error (BSSE) at different basis set levels.
• Comparative studies with semiempirical and ab initio methods at the 6-31G* basis set.
• Evaluation of M06-2X and M06-L DFT functionals.

Main Results:

• Accurate MP2 and CCSD(T) CBS interaction energies were obtained for 20 S22 dimers.
• BSSE significantly affects dispersion energy calculations, particularly with smaller basis sets.
• Aug-cc-pVTZ and aug-cc-pVQZ basis sets are needed for accurate BSSE-uncorrected CBS extrapolations.
• MP2 and CCSD(T) CBS energies agree well, except for aromatic systems.
• M06-2X and M06-L DFT functionals demonstrated superior accuracy compared to other tested methods.
• Discontinuities in interaction energy curves were resolved by using finer DFT numerical grids.

Conclusions:

• High-level ab initio calculations provide reliable interaction energies for molecular dimers.
• Careful consideration of BSSE is essential for accurate dispersion energy calculations.
• The M06-2X and M06-L functionals show promise for accurate DFT-based interaction energy studies.
• Finer DFT grids are necessary to avoid discontinuities in interaction energy calculations.