  A hierarchy of wavefunction composite methods (cWFT), based on G4- type cWFT
methods available for elements H through Rn, was recently reported by Semidalas
and Martin [J. Chem. Theor. Comput. 2020, 16, 4238]. We extend this hierarchy
by considering the inner-shell correlation energy in the second-order
Moller-Plesset correction and replacing the Weigend-Ahlrichs def2-mZVPP(D)
basis sets used in the aforementioned paper with complete basis set
extrapolation from augmented correlation consistent core-valence triple-zeta,
aug-cc-pwCVTZ(-PP), and quadruple-zeta, aug-cc-pwCVQZ(-PP), basis sets, thus
creating cc-G4- type methods. For the large and chemically diverse GMTKN55
benchmark suite, they represent a substantial further improvement and bring
WTMAD2 (weighted mean absolute deviation) down below 1 kcal/mol. Intriguingly,
the lion's share of the improvement comes from better capture of valence
correlation; the inclusion of core-valence correlation is almost an order of
magnitude less important. These robust correlation consistent cWFT methods
approach the CCSD(T) complete basis limit with just one or a few fitted
parameters. Particularly the DLPNO variants such as cc-G4-T-DLPNO are
applicable to fairly large molecules at modest computational cost, as is (for a
reduced range of elements) a different variant using MP2-F12/cc-pVTZ-F12 for
the MP2 component.
