The CABS singles correction is not used in this extrapolation. The HF limit can also be approximated by taking the HF energy evaluated with the largest available F12 specific basis set (aug-cc-pVQZ-PP-F12 in this case) and adding the CABS singles correction. The two approaches of using either Eqn. 3 to extrapolate the aug-cc-pVTZ-PP-F12 and augcc-pVQZ-PP-F12 results [denoted CBS(T,Q) herein], or aug-cc-pVQZ-PP-F12 plus CABS correction (QZ+CABS), are briefly compared below.