Our first choice was a DLPNO-CCSD(T 0 )/TightPNO/CBS (3,4) extrapolation with aug-cc-pVTZ/aug-cc-pVQZ, 177,178 followed by the equivalent extrapolation with the ma-def2-TZVPP/ma-def2-QZVPP 179 basis sets. Both of these levels of theory used the original semicanonical (T 0 ) procedure for the triples correction. The third option was to use a composite scheme based on MP2, which is corrected with the difference in corre-lation energy between MP2 and DLPNO-CCSD(T 0 ) (CC) calculated with a small basis set: