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XVII.C.1.

Calculated Ionization Energy for C2H2 (Acetylene)

Experimental Ionization Energy is 11.4 ± 0.002 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
composite G4 11.398
CBS-Q 11.409

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 aug-cc-pVDZ aug-cc-pVTZ cc-pV(T+d)Z
hartree fock HF 8.637 10.026 10.026 9.812 9.628 9.622   9.770 9.779 9.590 9.802 9.703 9.755 9.736 9.760 9.755
density functional LSDA 10.834 12.100 12.100 11.898 11.807 11.811 11.980 12.064 12.077 11.845   11.920 12.081 12.011   12.081
SVWN   12.100     11.807   11.980                  
BLYP 9.894 11.087 11.087 10.906 10.803 10.807 11.021 11.062 11.078 10.840   10.933 11.100     11.100
B1B95 10.171 11.301 11.301 10.620 10.949 10.982 11.130 11.161 11.173 11.000   11.079 11.138 11.110   11.138
B3LYP 10.078 11.282 11.282 11.087 10.969 10.971 11.153 11.200 11.215 10.994 11.245 11.085 11.226 11.180 11.240 11.226
B3LYPultrafine         10.969                      
B3PW91 10.157 11.363 11.363 11.134 11.009 11.011 11.149 11.198 11.210 11.023   11.104 11.206     11.206
mPW1PW91 10.113 11.303 11.325 11.095 10.942 10.943 11.087 11.123 11.156 10.973   11.036 11.134     11.134
M06-2X         11.027                      
PBEPBE 10.093 11.296 11.296 11.094 10.980 10.983 11.160 11.191 11.204 11.003   11.093 11.220     11.220
PBE1PBE         10.951                      
HSEh1PBE         10.933                      
TPSSh             11.015                  
Moller Plesset perturbation MP2 9.558 11.088 11.088 10.919 10.968 11.009 11.159 11.207 11.260 11.225 11.266 11.162 11.446 11.303 11.490 11.446
MP2=FULL 9.559 11.090 11.090 10.922 10.979 11.023 11.171 11.221 11.274 11.247   11.172 11.478 11.312 11.523 11.478
MP3         10.662   10.872                  
MP3=FULL         10.673   10.856                  
MP4   10.982     10.861       11.149       11.340      
Configuration interaction CID   10.743 10.743 10.557 10.527     10.730                
CISD     10.754 10.559 10.543     10.743                
Quadratic configuration interaction QCISD   10.910 10.910 10.726 10.730 10.769 10.901 10.938 10.988 10.944   10.893 11.138     11.138
QCISD(T)         10.815             10.986 11.265      
Coupled Cluster CCD   10.888 10.888 10.704 10.697 10.736 10.868 10.908 10.958 10.919   10.866 11.114      
CCSD(T)         10.810             10.981 11.261 11.114 11.300 11.261
CCSD(T)=FULL         10.821               11.295 11.122 11.335 11.295

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 9.724 9.516 9.919 9.720 9.951 9.957
density functional B3LYP 10.927 10.789 11.107 10.988 11.226 11.217
Moller Plesset perturbation MP2 10.768 10.832 11.020 11.073 11.035 11.041
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.