National Institute of Standards and Technology
Computational Chemistry Comparison and Benchmark DataBase
Release 22May 2022
NIST Standard Reference Database 101
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IV.D.4. (XII.A.2.)

Comparison of experiment and theory for rMgMg

Species with coordinate rMgMg
Species Name
Mg2 Magnesium diatomic
The small prefix is the number of bonds with completed calculations.
Click on an entry for a histogram of the difference distribution.
rms differences (calculated - experiment) in Å
Methods with predefined basis sets
semi-empirical AM1 1 0.903
PM3 2 1.548
PM6 1 2.185
composite G2 2 1.366
G3 2 3.109
G3B3 2 0.209
G4 1 1.208
CBS-Q 2 1.366
rms differences (calculated - experiment) 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 daug-cc-pVTZ
hartree fock HF 1 1.024 2 1.360 2 1.392 2 1.356 2 1.366 2 1.366 2 1.361 2 3.109 1 3.069 2 1.373 2 2.178 1 3.631 1 3.605 1 3.572 1 3.563 1 3.603 1 3.569 1 3.562 1 3.452
density functional LSDA 2 1.247 2 0.629 2 0.704 2 0.485 2 0.510 2 0.510 2 0.508 2 0.513 2 0.513 2 0.535   1 0.480 2 0.505 2 0.520   2 0.506 1 0.518    
BLYP 1 1.176 2 0.223 2 0.482 2 0.163 3 0.698 2 0.030 2 0.027 2 0.034 2 0.033 2 0.122   1 5.023 1 0.015 1 0.021   2 0.026      
B1B95 2 1.172   2 0.515 2 0.128 2 0.212 2 0.224 2 0.224 2 0.207 2 0.207 2 0.248   1 0.226 2 0.217 2 0.188   2 0.209 1 0.189    
B3LYP 1 1.165 2 0.311 2 0.437 2 0.264 2 0.035 2 0.035 2 0.038 2 0.036 1 0.036 2 0.055 2 0.011 1 5.542 2 0.035 1 0.045 2 0.051 1 0.026 2 0.035 2 0.046  
B3LYPultrafine         2 0.035             1 5.962 1 0.039 1 0.046   1 0.028 1 1.208    
B3PW91 1 1.187 2 0.189 2 0.528 2 0.219 2 0.287 2 0.287 2 0.285 2 0.282 1 0.281 2 0.307   1 0.089 1 0.286 1 0.283   2 0.288      
mPW1PW91 2 0.754 2 0.204 1 0.527 2 0.231 2 0.299 2 0.299 2 0.299 2 0.294 2 0.292 2 0.313   1 0.116 1 0.298 1 0.291   2 0.300 1 0.291    
M06-2X 1 1.153 1 0.078 2 0.450 1 0.074 2 0.108 1 0.108 1 0.107 1 0.105 1 0.105 1 0.142 1 0.075 1 0.310 1 0.102 1 0.094   1 0.103 1 0.093    
PBEPBE 1 1.209 2 0.398 1 0.607 1 0.354 2 0.392 2 0.392 2 0.392 2 0.390 2 0.390 2 0.412 2 0.398 1 0.300 2 0.391 2 0.389   1 0.393 1 0.388    
PBEPBEultrafine         2 0.390             1 0.299 1 0.389 1 0.387   1 0.392 1 0.387    
PBE1PBE 1 1.191   1 0.543 1 0.250 1 0.314 1 0.314 1 0.313 1 0.308 1 0.308 1 0.329   1 0.147 1 0.314 1 0.306   1 0.315 1 0.305    
HSEh1PBE 1 1.188 2 0.249 1 0.552 1 0.257 2 0.320 1 0.320 1 0.320 1 0.315 1 0.315 1 0.338   1 0.153 1 0.318 2 0.315   1 0.320 1 0.313    
TPSSh   1 0.186 1 0.532 1 0.262 1 1.208 1 0.336 1 1.208 1 0.335   1 1.208   1 0.128 1 0.341 1 1.208   1 0.343 1 0.339    
wB97X-D     1 1.208   1 1.208   1 1.208   1 1.208     1 1.208 1 1.208 1 1.208     1 1.208    
B97D3   1 1.208     1 1.208   1 1.208   1 1.208   1 1.208 1 0.105   1 1.208     1 0.208   1 0.209
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 daug-cc-pVTZ
Moller Plesset perturbation MP2 1 1.043 2 1.305 2 0.056 2 1.293 3 1.286 2 1.324 2 0.554 3 0.810 2 0.506 2 1.332   2 2.200 2 0.743 1 0.243 2 0.243 1 0.577 2 0.248 2 0.245  
MP2=FULL 1 1.069 2 1.306 1 0.169 1 1.359 2 0.502 2 0.500 2 1.338 2 0.424 1 0.427 1 0.109   1 2.148 1 0.932 1 0.932 2 0.197 2 0.756 2 0.659 1 0.277  
MP3         2 0.354   1 1.208         1 1.922 1 0.556 1 0.123          
MP3=FULL         1 1.208   1 0.310         1 1.872 1 0.545 1 0.132          
MP4   1 1.162     2 1.221     2 0.338 1 0.339     1 1.873 1 0.608 2 0.066   1 0.382 1 0.071    
MP4=FULL   1 1.138     1 0.264       1 0.274       1 0.596 1 0.185   1 0.353 1 0.228    
B2PLYP         1 0.315                 1 1.208          
B2PLYP=FULLultrafine         1 0.277               1 0.306 1 0.082     1 0.057    
Configuration interaction CID   1 1.261 1 0.578 1 1.823 1 0.915     2 0.920                      
CISD   1 1.253 1 0.612 1 1.822 1 0.917     1 0.969                      
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 daug-cc-pVTZ
Quadratic configuration interaction QCISD   2 1.232 1 0.776 1 1.970 2 1.296 1 1.463 2 1.358 2 1.296 1 1.298 1 0.657   1 1.949 2 1.519 2 0.679   1 1.119 1 0.633    
QCISD(T)         1 0.870     1 0.646       1 1.893 1 1.058 1 0.166   1 0.642 1 0.163    
Coupled Cluster CCD   1 1.342 1 0.752 1 1.983 2 1.315 1 1.418 1 1.293 2 1.251 1 1.245 1 0.597   1 1.902 2 1.490 1 0.620 1 0.508 1 1.055 1 0.589 1 0.511  
CCSD         2 1.300     2 1.285       1 1.952 1 1.513 1 0.687 1 0.557 1 1.118 1 0.646 1 0.554  
CCSD=FULL         1 1.269             1 1.903 1 1.399 1 0.120 1 0.252 1 0.980 1 0.024 1 0.220  
CCSD(T)         2 0.870 2 1.096   2 0.645     2 0.127 1 1.887 2 1.055 2 0.168 1 0.085 2 0.641 2 0.165 1 0.087  
CCSD(T)=FULL         1 0.766             1 1.838 1 0.995   1 0.070 1 0.580 1 0.194 1 0.093  
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 daug-cc-pVTZ
rms differences (calculated - experiment) in Å
Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD cc-pVTZ-PP aug-cc-pVTZ-PP Def2TZVPP
hartree fock HF 2 2.066 1 3.604 1 3.614 1 3.603 1 3.613 2 3.109     1 1.208
density functional B1B95 2 0.061 1 0.152              
B3LYP 1 0.250 1 0.088 1 0.246 1 0.078 1 0.071 1 0.264     1 1.208
PBEPBE                 1 1.208
Moller Plesset perturbation MP2 1 1.475 1 0.550 2 1.343 2 0.404 2 1.410 1 1.415     1 1.208
For descriptions of the methods (AM1, HF, MP2, ...) and basis sets (3-21G, 3-21G*, 6-31G, ...) see the glossary in section I.C. Predefined means the basis set used is determined by the method.