THE EFFECTS OF NONLOCAL GRADIENT CORRECTIONS IN DENSITY-FUNCTIONAL CALCULATIONS OF HYDROCARBON RADICAL HYPERFINE STRUCTURES

Ground-state equilibrium geometries and hyperfine structures of a number of organic neutral and charged radical compounds are computed using the linear combination of Gaussian-type orbitals-density functional theory method. In addition to the local spin-density approximation, we also use two different nonlocal (gradient corrected) schemes for the calculations of the exchange and correlation potentials. The different functional forms are found to generate slightly different total and unpaired spin-density distributions in the molecules, and as a result, the computed isotropic hyperfine coupling constants vary markedly. The smallest variations are found for the hydrogens, where the results are generally in satisfactory agreement with experiment. For the carbon atoms, however, large differences in isotropic coupling constants are observed. The anisotropic hyperfine structures are generally very well described at all levels of theory. (C) 1994 John Wiley & Sons, Inc.