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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 KBr atoms 1 and 2

For KBr (Potassium Bromide)
Bond length differences (full - frozen) in Å. Mouse over a difference for the bond length with full correlation.
Methods with standard basis sets
3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G*
Moller Plesset perturbation MP2=FULL 0.0044 0.0324 0.0001 0.0033 0.0031 0.0029 0.0074
MP3=FULL       -0.0036   -0.0331  
Coupled Cluster CCSD(T)=FULL       0.0030      
3-21G 3-21G* 6-31G 6-31G* 6-31G** 6-31+G** 6-311G*

kbr.gif