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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 C2- atoms 1 and 2

For C2- (carbon diatomic anion)
Bond length differences (full - frozen) in Å. Mouse over a difference for the bond length with full correlation.
Methods with standard basis sets
6-31G* 6-31+G** cc-pVQZ aug-cc-pVQZ
Moller Plesset perturbation MP3=FULL   -0.0017    
Coupled Cluster CCSD(T)=FULL 0.0015   0.0038 0.0039
6-31G* 6-31+G** cc-pVQZ aug-cc-pVQZ

c2q1.gif