VALIDATION OF SELF-CONSISTENT HYBRID DENSITY FUNCTIONALS FOR THE STUDY OF STRUCTURAL AND ELECTRONIC CHARACTERISTICS OF ORGANIC PI-RADICALS

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. © 1995 American Institute of Physics.