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

For CH+ (Methylidyne 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 cc-pVQZ aug-cc-pVDZ aug-cc-pVQZ cc-pV(T+d)Z
Moller Plesset perturbation MP2=FULL -0.000338 -0.001531 -0.001531 -0.001208 -0.003526 -0.003656 -0.003762 -0.017280 -0.017403 -0.003878 -0.001588 -0.010530 -0.024617 -0.001719 -0.024909 -0.010530
MP3=FULL         -0.003463   -0.004603                  
Coupled Cluster CCSD(T)=FULL         -0.003379               -0.025667   -0.025978  
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 cc-pVQZ aug-cc-pVDZ aug-cc-pVQZ cc-pV(T+d)Z