Accurate prediction for electron affinities of the radicals derived from the halide benzene

The molecular structures and electron affinities of eight radicals derived from the halide benzene by removing a hydrogen atom have been determined using seven hybrid Hartree-Fock/density-functional methods. The basis set used in this work is of double-zeta plus polarization quality with additional diffuse s- and p-type functions, denoted as DZP++. These methods have been carefully calibrated [J. C. Rienstra-Kiracofe, G. S. Tschumper, H. F. Schaefer, S. Nandi, and G. B. Ellison, Chem. Rev. (Washington, D. C.) 102, 231 (2002)]. The geometries are fully optimized with each density-functional theory method and discussed, respectively. The three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affinity, the vertical electron affinity, and the vertical detachment energy. The most reliable adiabatic electron affinities (with zero-point vibrational energy correction), obtained at the DZP++ B3LYP level of theory, are 1.74 eV (o-C6H4F), 1.39 eV (m-C6H4F), 1.34 eV (p-C6H4F), 1.78 eV (o-C6H4Cl), 1.53 eV (m-C6H4Cl), 1.45 eV (p-C6H4Cl), 2.06 eV (o-C6H3F2), and 2.04 eV (p-C6H3F2), respectively. Compared with the experimental values, the average absolute error of the B3LYP method is 0.03 eV. The BLYP, BP86, and BPW91 functionals also gave excellent predictions, with average absolute errors of 0.05, 0.08, and 0.08 eV, respectively.