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XVII.C.1.

Calculated Ionization Energy for C2 (Carbon diatomic)

Experimental Ionization Energy is 11.4 ± 0.3 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  
PM6  
composite G4 11.945
CBS-Q 11.912

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) TZVP cc-pVDZ cc-pVTZ cc-pVQZ aug-cc-pVDZ aug-cc-pVTZ aug-cc-pVQZ
hartree fock HF 6.012 8.069 8.069 7.766 7.724 7.724 7.809 7.791 7.791 7.632 7.836 7.757 7.755 7.764 7.709 7.755 7.762
density functional LSDA 10.418 12.324 12.324 12.058 11.932 11.932 12.059 12.145 12.145 11.889   11.985 12.137   11.996    
SVWN   12.324         12.059                    
BLYP 9.292 11.184 11.184   10.824       11.042 10.790   10.907 11.060        
B1B95 9.189 11.031 11.031 10.792 10.575 10.679 10.788 10.794 10.794 10.628   10.714 10.690        
B3LYP 9.180 11.072 11.072 10.813 10.698 10.698 10.837 10.877 10.877 10.652 10.924 10.763 10.882 10.895 10.779 10.886 10.896
B3LYPultrafine         10.698                        
B3PW91 9.201 11.084 11.084 10.787 10.681 10.681 10.778 10.807 10.807 10.626   10.718 10.806        
mPW1PW91 9.072 10.935 10.956 10.658 10.534 10.534 10.637 10.651 10.670 10.497   10.569 10.657   10.575    
M06-2X         10.436                        
PBEPBE 9.490 11.369 11.369 11.110 10.990 10.990 11.123 11.151 11.151 10.944   11.047 11.170   11.062 11.177  
PBEPBEultrafine         10.990                        
PBE1PBE         10.568                        
HSEh1PBE         10.453                        
TPSSh             10.679                    
Moller Plesset perturbation MP2 9.923 11.919 11.919 11.676 11.653 11.653 11.752 11.849 11.849 11.893 11.860 11.741 12.087 12.228 11.791 12.135 12.254
MP2=FULL   11.923     11.674 11.674 11.773 11.869 11.869     11.756 12.147 12.273 11.807    
MP3         10.035                        
MP3=FULL         10.052   10.138                    
MP4         11.659               12.054        
B2PLYP         12.163                        
Configuration interaction CID         9.966     10.089                  
CISD         10.108                        
Quadratic configuration interaction QCISD   11.282     10.937 10.937 11.016 11.063 11.063     10.986 11.247        
QCISD(T)         11.301                        
Coupled Cluster CCD         10.592     10.720       10.644          
CCSD         10.824                        
CCSD(T)         11.277             11.335 11.652   11.373 11.689  
CCSD(T)=FULL         11.301             11.347 11.724   11.387 11.778  

Ionization Energies in eV
Methods with effective core potentials (select basis sets)
CEP-31G CEP-31G* CEP-121G CEP-121G* LANL2DZ SDD
hartree fock HF 7.702 7.661 7.732 7.758 7.884 7.877
density functional B3LYP 10.518 10.434 10.543 10.525 10.932 10.903
Moller Plesset perturbation MP2 11.314 11.333 11.556 11.614 11.760 11.766
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.