THE HYPERFINE STRUCTURES OF SMALL RADICALS FROM DENSITY-FUNCTIONAL CALCULATIONS

The isotropic and anisotropic hyperfine (hf) structures of a set of an ionic, neutral and cationic radicals are investigated by means of loca l and nonlocal gradient-corrected density functional theory (DFT). The molecules under study are formed by H, C, N, O, F, and CI atoms, and the hf structures are computed at both the experimental (where present ) and various DFT and CI optimized geometries. The agreement with expe riment and with results from previous CI or MRCI calculations is gener ally very satisfactory. The anisotropic hf couplings are relatively in sensitive to basis set effects and functional form, whereas the isotro pic hf couplings are highly dependent on the form of the nonlocal corr ections to the exchange functional, particularly for heteroatoms. Usin g the functional by Perdew and Wang (''PW86''), an excellent agreement with experiment is obtained for all neutral and cationic radicals, wh ereas for the halide containing anions somewhat elongated bond lengths , and thus less accurate hf structures, are obtained.