Evaluating Cost and Accuracy in Two-Point Complete Basis Set Extrapolation Schemes Using Efficient Diffuse Basis Sets

A widely used procedure for obtaining the complete basis set (CBS) limit of an electronic structure method is to extrapolate results from a sequence of correlation-consistent basis sets. A recent study by Xi et al. [J. Phys. Chem. A 2024, 128, 3742−3749] trained two-point extrapolation schemes against a new extensive dataset using aug-cc-pVXZ (X = D, T, Q, 5, and 6) basis set pairs. Their results were very promising, providing a significant improvement over previous two-point extrapolation schemes. The present work shows that equally good results can be obtained at lower cost by using the smaller jun-cc-pVXZ or jul-cc-pVXZ basis sets, which contain fewer diffuse functions. Using the smaller jun and jul basis sets to extrapolate to the CBS limit provides a good compromise between accuracy and computational cost.