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

For Mg2+ (magnesium diatomic 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-pVQZ cc-pV(T+d)Z
Moller Plesset perturbation MP2=FULL -0.036187 -0.007775 -0.013948 -0.005888 -0.013068 -0.013068 -0.013918 -0.256219 -0.256219 -0.018255 -0.007300 -0.038021 -0.058762 -0.059615 -0.038021
MP3=FULL         -0.013167   -0.014291                
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-pVQZ cc-pV(T+d)Z