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

For H2CO3 (Carbonic acid)

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 -0.000674 -0.007137 -0.007137 -0.004490 -0.013134 -0.013427 -0.014186 -0.075202 -0.075425 -0.031327 -0.009124 -0.055173 -0.010732 -0.063418
MP3=FULL         -0.012478   -0.030681              
Coupled Cluster CCSD(T)=FULL         -0.012507           -0.008380 -0.055681 -0.009972 -0.064510
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