A systematic application of density functional theory to some carbon-containing molecules and their anions

Eight medium-sized carbon-containing molecules: linear carbon chains C-n (n = 6-9), triacetylene (C6H), tetracyanoethylene (C6N4), 1,1,1-trifluoroacet one enolate (CF3CHCHO), and C4O have been studied using six different densi ty functional or hybrid Hartree-Fock density functional methods with a doub le-zeta basis set with polarization and diffuse functions (DZP++). Optimize d geometries, harmonic vibrational frequencies, and adiabatic electron affi nities were estimated and compared to known experimental values. The harmon ic vibrational frequencies showed an overall agreement with experimental fu ndamentals of approximately 4-6% with one exception, the BHLYP functional. Average absolute errors in electron affinities estimated with the BP86, BLY P, and B3LYP functionals all show agreement of better than 0.2 eV with expe riment and provide a viable method of predicting electron affinities for mo lecules of the same type as studied here.