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

Geometry Comparison

Mg2 (Magnesium diatomic)


distance is atom 1 (Mg) to atom 2 (Mg)

Experimental bond length is 3.891  Å

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Calculated bond length in Å
Methods with predefined basis sets
semi-empirical AM1 dnf
PM3 2.342
PM6 1.705
composite G2 2.524
G3 7.000
G3B3 4.185
G4 2.683
CBS-Q 2.524

Calculated bond length in Å
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) 6-311+G(3df,2p) TZVP cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ
hartree fock HF 2.866 2.531 2.499 2.535 2.524 2.524 2.529 dnf 6.960 2.518 dnf 7.522 7.495 7.462 7.454 7.493 7.459 dnf
density functional LSDA 2.643 3.186 3.186 3.406 3.381 3.381 3.382 3.377 3.377 3.355   3.411 3.385 3.371   3.385 3.373  
SVWN   3.347     3.381 3.381 3.382 3.377 3.377 3.355     3.385 3.371   3.385 3.373  
BLYP 2.714 4.114 3.408 4.053 3.861 3.861 3.864 3.857 3.858 3.769   dnf 3.876 3.870   3.864    
B1B95 2.718 3.845 3.375 3.762 3.679 3.667 3.667 3.684 3.684 3.642   4.117 3.674 3.703   3.682 3.702  
B3LYP 2.725 4.201 3.454 4.154 3.926 3.926 3.929 3.927 3.927 3.836 3.902 9.432 3.926 3.935 3.941 3.916 3.926 3.936
B3LYPultrafine         3.926             9.852 3.930 3.937   3.919 2.683  
B3PW91 2.704 3.702 3.363 3.672 3.604 3.604 3.605 3.608 3.609 3.583   3.802 3.604 3.608   3.603    
mPW1PW91 3.137 3.687 3.364 3.659 3.592 3.592 3.592 3.597 3.599 3.577   3.775 3.592 3.599   3.590 3.600  
M06-2X 2.737 3.969 3.440 3.816 3.782 3.782 3.783 3.785 3.785 3.749   4.200 3.788 3.796   3.787 3.797  
PBEPBE 2.681 3.492 3.284 3.537 3.499 3.499 3.499 3.500 3.500 3.479 3.492 3.591 3.500 3.502   3.497 3.502  
PBEPBEultrafine         3.500             3.591 3.501 3.503   3.499 3.503  
PBE1PBE 2.700 3.347 3.347 3.640 3.577 3.577 3.577 3.582 3.582 3.562   3.743 3.577 3.584   3.576 3.585  
HSEh1PBE 2.702 3.642 3.338 3.634 3.570 3.570 3.571 3.576 3.576 3.552   3.738 3.572 3.576   3.571 3.577  
TPSSh   3.705 3.359 3.629 2.683 3.554 2.683 3.555       3.763 3.550 2.683   3.548 3.551  
Moller Plesset perturbation MP2 2.847 2.586 3.946 2.598 2.567 2.567 4.444 4.396 4.396 2.558   6.071 4.634 4.133 4.188 4.468 4.138 4.188
MP2=FULL 2.821 2.584 3.722 5.249 4.393 4.390 2.552 4.314 4.317 3.782   6.038 2.959 2.959 4.169 2.959 2.959 4.167
MP3         4.245   2.683         5.813 4.446 4.013        
MP3=FULL         2.683   4.200         5.762 4.435 3.759        
MP4   5.053     2.670     4.229 4.229     5.763 4.498 3.957   4.273 3.961  
MP4=FULL   5.029     4.155       4.165       4.486 3.705   4.243 3.663  
B2PLYP         4.205                 2.683        
Configuration interaction CID   5.151 4.469 5.714 4.806     4.810                    
CISD   5.144 4.502 5.712 4.807     4.859                    
Quadratic configuration interaction QCISD   2.659 4.667 5.861 2.595 5.353 dnf dnf 5.188 4.547   5.840 5.409 4.570   5.009 4.524  
QCISD(T)         4.760     4.537       5.783 4.949 4.056   4.532 4.053  
Coupled Cluster CCD   5.233 4.643 5.873 2.575 5.308 5.184 dnf 5.136 4.488   5.793 5.380 4.511 4.399 4.946 4.479 4.402
CCSD         2.590     5.175       5.842 5.403 4.577 4.447 5.008 4.536 4.444
CCSD=FULL         5.160             5.794 5.289 4.011 4.142 4.870 3.914 4.111
CCSD(T)         4.761 2.608   4.535     4.018 5.777 4.945 4.059 3.975 4.532 4.056 3.977
CCSD(T)=FULL         4.657             5.728 4.885   3.820 4.470 3.697 3.798

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 dnf 7.494 7.504 7.494 7.504 dnf
density functional B1B95 3.829 3.738        
B3LYP 4.140 3.978 4.137 3.969 3.961 4.154
Moller Plesset perturbation MP2 5.366 4.440 dnf 4.294 dnf 5.305
Values that are outliers may reflect incorrect atom numbering for different levels of theory.
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