National Institute of Standards and Technology
Computational Chemistry Comparison and Benchmark DataBase
Release 22May 2022
NIST Standard Reference Database 101
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XVII.C.1. (III.D.6.)

Calculated Ionization Energy for O2 (Oxygen diatomic)

Experimental Ionization Energy is 12.0697 ± 0.0002 eV
Please note! These calculated ionizataion energies have the vibrational zero-point energy (zpe) included, but the zpe has NOT been scaled. Click on an entry for more details, including the ionization energy with a scaled zpe.
Original data displayed. Press to display differences.
Differences displayed. Press to display original data.
Ionization Energies in eV
Methods with predefined basis sets
semi-empirical PM3  
composite G2 12.201
G3 12.276
G3B3 12.114
G4 12.045
CBS-Q 12.270
Ionization Energies in eV
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 cc-pV(T+d)Z daug-cc-pVTZ
hartree fock HF 11.123 13.548 13.548 13.382 12.406 12.406 12.442 12.274 12.274 12.145   12.262 12.215 12.130 12.127 12.290 12.172 12.141 12.131 12.166
ROHF   13.171 13.548 12.910 11.870 11.870 11.876 11.755 12.274       11.705 11.551 12.127 12.291 12.172 12.141    
density functional LSDA 10.881 13.408 13.408 13.497 12.858 12.858 13.016 12.877 12.877 12.683     12.701 12.789   12.907 12.851   12.789  
BLYP 10.355 12.728 12.728 12.868 12.242 12.242 12.454 12.267 12.267 12.064   12.344 12.092 12.215         12.215  
B1B95 10.865 13.185 13.185 13.131 12.286 12.397 12.505 12.349 12.349 12.091   12.385 12.241 12.140   12.275 12.195      
B3LYP 10.931 13.267 13.267 13.300 12.601 12.601 12.752 12.582 12.583 12.406   12.625 12.443 12.503 12.523 12.639 12.571 12.550 12.503  
B3LYPultrafine         12.601             12.626 12.443 12.503   12.639 12.571      
B3PW91 10.974 13.364 13.364 13.289 12.572 12.572 12.669 12.531 12.531 12.380   12.533 12.427 12.429         12.429  
mPW1PW91 11.033 13.377 13.405 13.306 12.546 12.546 12.646 12.496 12.519 12.376   12.536 12.401 12.399   12.563 12.478   12.399  
M06-2X 11.033 13.451 13.451 13.343 12.531 12.531 12.628 12.534 12.534 12.344 12.496 12.503 12.367 12.455   12.506 12.502      
PBEPBE 10.417 12.856 12.856 12.895 12.244 12.244 12.410 12.241 12.241 12.075   12.303 12.107 12.188   12.318 12.269   12.188  
PBEPBEultrafine         12.244             12.303 12.107 12.188   12.318 12.269      
PBE1PBE 10.927 13.326 13.326 13.243 12.504 12.504 12.607 12.453 12.453 12.314   12.480 12.359 12.369   12.500 12.428      
HSEh1PBE 10.923 13.315 13.315 13.239 12.501 12.501   12.454 12.454 12.308   12.483 12.352 12.370   12.496 12.428      
TPSSh   13.188 13.188 13.119 12.413 12.413 12.518 12.379   12.224   12.409 12.277 12.296   12.415 12.354      
wB97X-D     13.367   12.545   12.627   12.486     12.449 12.853 12.324     12.368      
B97D3   13.147     12.399   12.534   12.383   12.386 12.430   12.308     12.380     12.377
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 cc-pV(T+d)Z daug-cc-pVTZ
Moller Plesset perturbation MP2 7.855 11.188 11.188 11.454 11.516 11.516 11.599 11.414 11.414 11.521   11.437 11.330 11.578 11.664 11.607 11.688 11.711 11.578  
MP2=FULL 7.853 11.185 11.185 11.451 11.514 11.514 11.598 11.417 11.417 11.520   11.441 11.328 11.575 11.677 11.606 11.679 11.723 11.575  
ROMP2         11.742 11.742 11.874 11.642 11.642 11.762   11.700 11.545 11.857   11.891        
MP3         12.120   12.319         11.969 11.854 12.085            
MP3=FULL         12.118   12.189         11.973 11.851 12.071            
MP4   11.482     11.710       11.551     11.595 11.490 11.727   11.806 11.860      
MP4=FULL         11.709       11.553       11.489 11.719   11.804 11.844      
B2PLYP 9.849 12.546 12.546 12.749 12.198 12.198 12.330 12.141 12.141 12.058   12.190 12.026 12.141   12.254 12.229      
B2PLYP=FULL 9.848 12.545 12.545 12.748 12.197 12.197 12.329 12.141 12.141 12.057   12.191 12.025 12.138   12.253 12.223      
B2PLYP=FULLultrafine         12.197                       12.223      
Configuration interaction CID   12.583 12.583 12.614 12.061     11.907                        
CISD   12.561 12.561 12.617 12.060     11.904                        
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 cc-pV(T+d)Z daug-cc-pVTZ
Quadratic configuration interaction QCISD   12.320 12.320 12.475 11.967 11.967 12.075 11.818 11.818 11.925   11.867 11.723 11.986   12.027 12.108   11.986  
QCISD(T)         11.876             11.776 11.630 11.901   11.957 12.039      
Coupled Cluster CCD   12.376 12.376 12.480 11.972 11.972 12.049 11.823 11.823 11.927   11.850 11.733 11.976   11.999 12.083      
CCSD         11.978             11.875 11.734 11.995 12.087 12.031 12.115 12.134    
CCSD=FULL         11.976             11.879 11.733 11.983 12.096 12.029 12.093 12.141    
CCSD(T)   12.200     11.879   11.992   11.723     11.780 11.634 11.906 12.011 11.958 12.043 12.064 11.906  
CCSD(T)=FULL         11.878             11.783 11.632 11.893 12.017 11.956 12.020 12.069    
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 cc-pV(T+d)Z daug-cc-pVTZ
Ionization Energies in eV
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 13.615 12.564 13.524 12.448 13.412 13.410     12.150
density functional LSDA 13.635 12.978 13.594 12.958 13.558 13.547      
B1B95 13.356 12.607 13.161 12.441 13.027 13.013      
B3LYP 13.553 12.802 13.478 12.758 13.379 13.362     12.543
PBEPBE                 12.234
Moller Plesset perturbation MP2 11.428 11.473 11.396 11.489 11.360 11.353     11.609
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.