Basis Set Requirements for Sulfur Compounds in Density Functional Theory:  a Comparison between...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate molecular property prediction relies on appropriate basis sets and theoretical methods.
• Basis set convergence is crucial for obtaining reliable computational results.
• The development of cost-effective basis sets is essential for widespread application.

Purpose of the Study:

• To evaluate the performance of polarization-consistent (pc) basis sets against correlation-consistent (cc) and Pople-type basis sets for SX, SO2, and SO3 molecules using the B3LYP functional.
• To assess the cost-benefit ratio of different basis sets for achieving high-quality computational results.
• To determine the reliability of pc basis sets for extrapolating to the Kohn-Sham complete basis set (CBS) limit.

Main Methods:

• Calculations were performed using the B3LYP density functional.
• A range of basis sets were employed, including correlation-consistent (cc), polarization-consistent (pc), and Pople-type sets.
• Extrapolation techniques were used to estimate the complete basis set (CBS) limit.

Main Results:

• Augmented pc basis sets (aug-pc) provide results of aug-cc-pV(5+d)Z and aug-cc-pV(6+d)Z quality at a significantly lower cost.
• Smaller pc basis sets yield results of nearly double-zeta quality, which are not reliable.
• The B3LYP functional struggles with precise CBS limit extrapolation using pc basis sets; ab initio methods perform better.
• For molecules like SO, SF, SO2, and SO3, cc basis sets are more effective than pc basis sets with B3LYP.
• Tight d functions are important; cc-pV6Z for SO2 yielded a total atomization energy 1 kcal/mol lower than aug-cc-pV(6+d)Z.

Conclusions:

• Aug-pc basis sets offer a compelling cost-benefit advantage for B3LYP calculations, approaching the accuracy of larger cc sets.
• Standard extrapolation methods with pc basis sets are less reliable for B3LYP CBS limits compared to ab initio approaches.
• Correlation-consistent basis sets remain the preferred choice for sulfur-containing molecules with highly electronegative elements.