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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 CN- atoms 1 and 2

For CN- (cyanide anion)
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 cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ cc-pCVTZ
Moller Plesset perturbation MP2=FULL 0.0001 0.0001 0.0001 0.0001 -0.0036 0.0012 0.0012 -0.0038 0.0009 0.0031 0.0010 0.0007 0.0040 0.0031 0.0009 0.0057 0.0031 0.0022
MP3=FULL         0.0010   0.0021       0.0008 0.0005 0.0035         0.0019
MP4=FULL   0.0001     0.0012       0.0009     0.0007 0.0042   0.0009 0.0061   0.0019
B2PLYP=FULL 0.0000 0.0072 0.0000 0.0000 0.0042 0.0003 0.0047 0.0003 0.0003 0.0009 0.0003 0.0002 -0.0009   0.0002 0.0015   0.0006
Quadratic configuration interaction QCISD(T)=FULL         0.0011             0.0006 0.0039   0.0008 0.0056   0.0019
Coupled Cluster CCSD=FULL         0.0010         0.0029 0.0009 0.0006 0.0038 0.0028 0.0008 0.0053 0.0029 0.0020
CCSD(T)=FULL         0.0011           0.0009 0.0006 0.0039 0.0028 0.0008 0.0056 0.0029 0.0020
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 cc-pCVTZ

cnq1.gif