National Institute of Standards and Technology
Computational Chemistry Comparison and Benchmark DataBase
Release 17bSeptember 2015
NIST Standard Reference Database 101
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XIXIndex of properties
XXH-bond dimers
XXIOddities

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XVII.C.1. (III.D.6.)

Calculated Ionization Energy for Si2 (Silicon diatomic)

Experimental Ionization Energy is 7.9 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 AM1  
PM3  
PM6  
composite G2 8.346
G3 8.439
G4 8.424
CBS-Q 8.350

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 3.385 7.741 7.895 7.714 7.304 7.303 7.280 7.300 7.300 7.266 8.886 7.246 7.787 7.790 7.803 7.240 7.248
density functional LSDA 5.357 4.962 8.908 8.989 8.851 8.851 8.863 8.837 8.837 8.804   8.810 8.825   8.830    
SVWN   8.977         8.866       8.847            
BLYP 4.440 8.064 8.021 7.939 7.884 7.970 8.001 8.117 8.065 7.934   7.930 7.943        
B1B95 4.663 4.905 8.466 8.293 8.352 8.367 8.372 8.337 8.337 8.263   8.356 8.223   8.356    
B3LYP 4.577 8.254 8.446 8.288 8.345 8.203 8.206 8.218 8.327 8.190 9.119 8.159 8.347 8.349 8.351 8.354 8.196
B3LYPultrafine         8.344                     8.354  
B3PW91 4.775 8.495 8.662 8.479 8.412 8.412 8.541 8.518 8.411 8.396   8.535 8.389        
mPW1PW91 5.884 8.492 8.662 8.481 8.407 8.520 8.548 8.381 8.408 8.545   8.537 8.380        
M06-2X     9.137   9.137                        
PBEPBE 4.758 8.469 8.238 8.401 8.135 8.186 8.138 8.167 8.141 8.127   8.131 8.067        
PBE1PBE         9.267                        
HSEh1PBE   9.405         8.382           8.367        
TPSSh         8.175   8.167     8.007     7.998        
wB97X-D     9.366   9.283       9.262       9.205     9.205  
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
Moller Plesset perturbation MP2 3.563 7.850 8.227 7.871 8.151 8.215 8.203 8.226 8.222 8.363 8.789 8.222 8.398 8.451 8.308 8.408 8.467
MP2=FULL   7.846 8.227 7.870 8.152 8.227 8.213 8.224 8.224     8.236 8.416 8.445      
MP3         8.062                        
MP3=FULL         8.790   8.085                    
MP4   7.646     8.065                        
B2PLYP         8.931               8.301        
Configuration interaction CID   7.714 8.057 7.649 7.833     7.842                  
CISD   7.745 8.063 7.642 7.860                        
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
Quadratic configuration interaction QCISD   7.805 8.068 7.617 7.981   7.939 7.961 7.958     7.948 8.263        
QCISD(T)         8.071             8.115 8.289   8.129    
Coupled Cluster CCD     8.056 7.625 7.971   7.887 7.909       7.891 8.251   8.145    
CCSD(T)         8.059             8.114 8.277   8.116    
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

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 7.711 7.782 7.673 7.772 8.039 7.677
density functional B3LYP 8.263 8.326 8.211 8.285 8.569 8.252
Moller Plesset perturbation MP2 7.809 8.169 7.828 8.189 8.070 7.791
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.