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. [<i>J. Phys. Chem. A</i> <b>2024</b>, <i>128</i>, 3742-3749] trained two-point extrapolation schemes against a new extensive dataset using aug-cc-pV<i>X</i>Z (<i>X</i> = 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-pV<i>X</i>Z or jul-cc-pV<i>X</i>Z 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.