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Energy differences between frozen core and all electrons correlated.
MP2, MP3, MP4, B2PLYP, CCSD, and CCSD(T)

For CH3CN+ (Acetonitrile cation)

Energies in Hartree
Methods with standard basis sets
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) cc-pVDZ cc-pVTZ aug-cc-pVDZ aug-cc-pVTZ
Moller Plesset perturbation MP2=FULL -0.001042 -0.004886 -0.004886 -0.003677 -0.012797 -0.013326 -0.013668 -0.055456 -0.055900 -0.024198 -0.007036 -0.043628 -0.008158 -0.050978
MP3=FULL         -0.012530   -0.016081              
Coupled Cluster CCSD(T)=FULL         -0.012467           -0.006492 -0.044688 -0.007589 -0.029171
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) cc-pVDZ cc-pVTZ aug-cc-pVDZ aug-cc-pVTZ