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

For NaK+ (Sodium Potassium 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) TZVP
Moller Plesset perturbation MP2=FULL -0.052733 -0.001878 -0.003414 -0.001512 -0.002195 -0.002195 -0.002286 -0.238159 -0.238159 -0.009020 -0.106125
MP3=FULL         -0.002179   -0.002266       -0.108528
MP4=FULL   -0.001937     -0.002309       -0.237443    
B2PLYP=FULL -0.017382 -0.000680 -0.001209 -0.000556 -0.000790 -0.000790 -0.000822 -0.070604 -0.070604 -0.002999 -0.033299
Quadratic configuration interaction QCISD(T)=FULL         -0.002304            
QCISD(TQ)=FULL         -0.002292   -0.002383        
Coupled Cluster CCSD=FULL         -0.002253         -0.009467 -0.111048
CCSD(T)=FULL         -0.002303           -0.112781
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) TZVP