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

For C6N4 (Tetracyanoethylene)

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) TZVP cc-pVDZ cc-pVTZ
Moller Plesset perturbation MP2=FULL -0.003293 -0.017021 -0.017021 -0.012913 -0.044633 -0.044633 -0.046474 -0.187654 -0.187654 -0.088429 -0.170771 -0.023178 -0.145953
MP3=FULL         -0.043836   -0.065631            
Coupled Cluster CCSD(T)=FULL         -0.043742             -0.021474  
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) TZVP cc-pVDZ cc-pVTZ