The effects of nonlocal gradient corrections in density functional calculations of hydrocarbon radical hyperfine structures

Abstract

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.

A density functional theory study of the free radicals NH2, NF2, NCl2, PH2, PF2, and PCl2

“…The particular version employed was slightly modified (16) to allow for partial inclusion of symmetry in the calculations. The hyperfine calculation routine is by Malkin and co-workers (12,13). The isotropic hf coupling on centre N is obtained from the equation and are indirectly related to the spatial distribution of the density.…”

“…These are loosely contracted to form the (5 1 11 1/21 1111) and (5 1 11 11 1/21 11 1111 1) bases, respectively (23). These basis sets have been employed with great success in a b initio and DFT calculations of nuclear magnetic resonance (NMR) parameters (23,24), as well as in previous DlT studies of hyperfine structures (12,13). The contracted basis sets will be referred to as IGLO-I1 and IGLO-111, respectively, from their original individual gauge of localized orbitals (IGLO) -NMR applications (23).…”

“…We have previously shown that DFT can yield highly accurate equilibrium geometries and isotropic hf couplings for hydrocarbon radical cations (1 1, 12) even at the local density level, whereas for heteroatoms a non-local description of the exchange and correlation functional is often required in order to reproduce experimental data (13).…”

“…We first outline the theoretical model used, although we refer to previous work (12,13) for more detailed descriptions of the hf calculations. For two excellent reviews, see also ref.…”

Mechanisms of Mutagenic DNA Nucleobase Damages and Their Chemical and Enzymatic Repairs Investigated by Quantum Chemical Methods

“…This is similar to that observed need in related studies on the methyl radical ( • CH 3 ) to slightly pyramidalize the carbon centre in order to obtain best agreement between the calculated and experimentally measured HFCCs. (Eriksson et al 1994) 6. Oxidative repair of alkylated nucleobases: the catalytic mechanism of AlkB A common type of DNA damage is the alkylation of nucleobases at one or more of their oxygen and nitrogen centres.…”