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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 AlN atoms 1 and 2

For AlN (Aluminum nitride)
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 cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ cc-pV(D+d)Z cc-pV(T+d)Z cc-pCVDZ cc-pCVTZ
Moller Plesset perturbation MP2=FULL -0.0006 -0.0006 0.0001 -0.0006 0.0323 0.0007 0.0008 0.0341 0.0010 0.0069 0.0004 0.0054 0.0289 0.0026 0.0078 0.0021 0.0068 0.0000 0.0044
MP3=FULL         -0.0286   -0.0080                        
B2PLYP=FULL         -0.0088   -0.0078                        
Coupled Cluster CCSD(T)=FULL         0.0003           0.0010 0.0047 0.0187 0.0013 0.0090 0.0003 0.0058 -0.0010 0.0034
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 cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ cc-pV(D+d)Z cc-pV(T+d)Z cc-pCVDZ cc-pCVTZ

alnq1.gif