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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 BeCl+ atoms 1 and 2

For BeCl+ (beryllium monochloride 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) cc-pVDZ cc-pVTZ aug-cc-pVDZ aug-cc-pVTZ cc-pV(T+d)Z
Moller Plesset perturbation MP2=FULL 0.0001 0.0000 0.0005 0.0002 0.0032 0.0032 0.0033 0.0016 0.0016 0.0072 0.0018 0.0098     0.0107
MP3=FULL         0.0019   0.0028                
Coupled Cluster CCSD(T)=FULL                     0.0016 0.0107 0.0039 0.0103  
STO-3G 3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G* 6-311G** 6-31G(2df,p) cc-pVDZ cc-pVTZ aug-cc-pVDZ aug-cc-pVTZ cc-pV(T+d)Z

beclq1.gif