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

For Li2O+ (dilithium oxide 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 cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ
Moller Plesset perturbation MP2=FULL -0.000605 -0.002288 -0.002288 -0.001562 -0.004073 -0.004073 -0.009495 -0.044980 -0.044980 -0.011194 -0.042707 -0.002662 -0.037357 -0.063018 -0.014534 -0.041607 -0.067191
MP3=FULL         -0.003863   -0.014867                    
Coupled Cluster CCSD(T)=FULL         -0.003887           -0.047215 -0.002482 -0.041808 -0.069159 -0.016285 -0.046470 -0.073886
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 cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ