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

Ground-state equilibrium geometries and hyperfine structures of a numb er of organic neutral and charged radical compounds are computed using the linear combination of Gaussian-type orbitals-density functional t heory method. In addition to the local spin-density approximation, we also use two different nonlocal (gradient corrected) schemes for the c alculations of the exchange and correlation potentials. The different functional forms are found to generate slightly different total and un paired spin-density distributions in the molecules, and as a result, t he 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 a toms, however, large differences in isotropic coupling constants are o bserved. The anisotropic hyperfine structures are generally very well described at all levels of theory. (C) 1994 John Wiley & Sons, Inc.