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Bond Length differences between FULL (all electrons correlated) and FROZEN core

Such as MP2=Frozen and MP2=Full
17 10 27 16 27

For NaK+ atoms 1 and 2

For NaK+ (Sodium Potassium diatomic cation)
Bond length differences (full - frozen) in Å. Mouse over a difference for the bond length with full correlation.
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 0.0205 0.0046 0.0280 0.0021 0.0098 0.0098 0.0103 0.0200 0.0200 0.0503 0.0210
MP3=FULL         0.0104   0.0109       0.0194
MP4=FULL   0.0054     0.0110       0.0207    
B2PLYP=FULL 0.0062 0.0014 0.0092 0.0008 0.0036 0.0036 0.0038 0.0069 0.0069 0.0162 0.0073
Quadratic configuration interaction QCISD(T)=FULL         0.0111            
Coupled Cluster CCSD=FULL         0.0109         0.0535 0.0201
CCSD(T)=FULL         0.0111           0.0200
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) TZVP

nakq1.gif