Predicting electron affinities with density functional theory: Some positive results for negative ions

The atomic electron affinities of the eight first row (H,Li,…,F) atoms as well as the adiabatic electron affinities of 12 first row diatomic and 15 first row triatomic molecules were determined using six different density functional or hybrid Hartree–Fock/density functional methods. The 35 species were selected for having relatively well-established experimental electron affinities. Harmonic zero-point vibrational energy corrected electron affinities are also reported for the diatomic and triatomic molecules. Equilibrium geometries and harmonic vibrational frequencies are given for the 27 molecules and their anions as determined with each density functional method. Discussion focuses on comparison of theoretical and experimental electron affinities. For the atomic, diatomic, and triatomic electron affinities the average absolute error is reported for each exchange–correlation functional. Since many of the molecular anion structures and vibrational frequencies are unknown, the work suggests new experimental directions.