Study of transition‐state methods in the calculation of vertical ionization potentials by local density approximation

The vertical ionization potentials of nine small molecules were computed by the deMon density functional program and different versions of the transition‐state method and the results were compared with earlier calculations and with experiment. The average absolute deviation of the 38 computed ionization potentials of the valence electrons of nine small molecules from experiment is 0.4 eV, which compares well with previous ab initio post‐Hartree–Fock and semi‐empirical HAM/3 calculations. The efficient methods were then used to calculate 68 ionization potentials of sixteen 22‐electron molecules, with results of similar quality.