ECBStotal=Fscf_scheme(Escf_basistotal,SCF)+Fcorl_scheme(Ecorl_basiscorl,corl_wfn)+δdelta_wfndelta_wfn_lesser+δdelta2_wfndelta2_wfn_lesser+δdelta3_wfndelta3_wfn_lesser+δdelta4_wfndelta4_wfn_lesser+δdelta5_wfndelta5_wfn_lesser

Here, F is an energy or energy extrapolation scheme, and the following also hold.

δdelta_wfndelta_wfn_lesser=Fdelta_scheme(Edelta_basiscorl,delta_wfn)−Fdelta_scheme(Edelta_basiscorl,delta_wfn_lesser)

δdelta2_wfndelta2_wfn_lesser=Fdelta2_scheme(Edelta2_basiscorl,delta2_wfn)−Fdelta2_scheme(Edelta2_basiscorl,delta2_wfn_lesser)

δdelta3_wfndelta3_wfn_lesser=Fdelta3_scheme(Edelta3_basiscorl,delta3_wfn)−Fdelta3_scheme(Edelta3_basiscorl,delta3_wfn_lesser)

δdelta4_wfndelta4_wfn_lesser=Fdelta4_scheme(Edelta4_basiscorl,delta4_wfn)−Fdelta4_scheme(Edelta4_basiscorl,delta4_wfn_lesser)

δdelta5_wfndelta5_wfn_lesser=Fdelta5_scheme(Edelta5_basiscorl,delta5_wfn)−Fdelta5_scheme(Edelta5_basiscorl,delta5_wfn_lesser)

A translation of this ungainly equation to example [5] below is as follows. In words, this is a double- and triple-zeta 2-point Helgaker-extrapolated CCSD(T) coupled-cluster correlation correction appended to a triple- and quadruple-zeta 2-point Helgaker-extrapolated MP2 correlation energy appended to a SCF/aug-cc-pVQZ reference energy.

ECBStotal=Fhighest_1(Eaug-cc-pVQZtotal,SCF)+Fcorl_xtpl_helgaker_2(Eaug-cc-pV[TQ]Zcorl,MP2)+δCCSD(T)MP2

δCCSD(T)MP2=Fcorl_xtpl_helgaker_2(Eaug-cc-pV[DT]Zcorl,CCSD(T))−Fcorl_xtpl_helgaker_2(Eaug-cc-pV[DT]Zcorl,MP2)