Validation of self-consistent hybrid density functionals for the study of structural and electronic characteristics of organic π radicals

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Abstract
Extensive density functional calculations are reported for the geometrical structures, thermochemistry, infrared, and hyperfine parameters of representative carbon‐centered π radicals. Local functionals can be considered sufficient for geometrical and vibrational parameters, but seriously fail in the computation of thermochemical data and of spin‐dependent properties. Gradient corrections (especially Becke exchange and Lee–Yang–Parr correlation functionals) sensibly improve matters. Inclusion of some Hartree–Fock exchange in a fully self‐consistent density functional implementation delivers a further significant improvement, approaching the accuracy of the most refined post Hartree–Fock computations. Purposely tailored basis sets are also introduced which are small enough to be used in molecular computations, but still give high quality geometries and hyperfine coupling constants.