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

For KO (Potassium monoxide)

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
Moller Plesset perturbation MP2=FULL -0.013499 -0.008376 -0.015140 -0.000956 -0.000864 -0.002325 -0.002592 -0.124348 -0.125542 -0.007510 -0.058241
MP3=FULL         -0.002120   -0.002381       -0.062019
MP4=FULL   -0.008146     -0.002138       -0.123515    
B2PLYP=FULL   -0.003293 -0.004649 -0.000278 -0.000675 -0.000675 -0.000752 -0.035545 -0.035545 -0.002164 -0.018823
Quadratic configuration interaction QCISD(T)=FULL         -0.002122            
QCISD(TQ)=FULL         -0.002120   -0.002378        
Coupled Cluster CCSD=FULL         -0.002096           -0.062983
CCSD(T)=FULL         -0.002122           -0.063514
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) TZVP