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IV.D.1. (XII.C.1.)

Geometry Comparison

I2 (Iodine diatomic)


distance is atom 1 () to atom 2 ()

Experimental bond length is 2.665  Å

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Calculated bond length in Å
Methods with predefined basis sets
semi-empirical AM1 2.538
PM3 2.668

Calculated bond length in Å
Methods with standard basis sets
3-21G 3-21G* 6-311G*
hartree fock HF 2.865 2.696 2.703
density functional BLYP 2.938 2.750 2.775
B1B95     2.694
B3LYP 2.902 2.719 2.737
B3PW91 2.877 2.691 2.706
mPW1PW91 2.868 2.684 2.698
PBEPBE 2.901 2.706 2.726
Moller Plesset perturbation MP2 2.918 2.711 2.714
MP2=FULL 2.918 2.709 2.718
MP3     2.731
MP4 2.948   2.739
Configuration interaction CID 2.938 2.715 2.712
CISD 2.942 2.716 2.713
Quadratic configuration interaction QCISD 2.954 2.727 2.733
QCISD(T)     2.744
Coupled Cluster CCD 2.949 2.725 2.730
CCSD(T)     2.744
CCSD(T)=FULL     2.746

Calculated bond length in Å
Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD
hartree fock HF 2.770   2.770   2.817 2.805
density functional B3LYP 2.823   2.823   2.863 2.853
Moller Plesset perturbation MP2 2.836   2.836   2.877 2.868
Values that are outliers may reflect incorrect atom numbering for different levels of theory.
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