Ab initio Study of the Spin Density of Nitroxide Radicals *

The spin densities of the nitroxides H 2 N O , (CH 3 )HNO and (CH 3 ) 2 NO have been studied by iterative CI methods. Calculations at different geometries with various basis sets were performed. It is found that the spin distribution is delocalized within the N O group, and substitution of the hydrogen atoms on the nitroxyl group by methyl groups changes the spin distribution significantly. Electron correlation, as well as the basis-set quality, plays an important role for the fluctuation of spin populations in the nitroxide radicals. It has been found that the spin density map can be predicted fairly well when correlation was included at certain levels and reasonable quality basis sets were employed. The spin polarization mechanism has been studied through a core excitation method. The superiority of local-spin-density (LSD) theory over the unrestricted Hartree-Fock (UHF) method in spin property studies is discussed.