A DENSITY-FUNCTIONAL THEORY STUDY OF HYPERFINE STRUCTURES OF NEUTRAL S,N-HETEROCYCLES

The electronic structures and isotropic hyperfine coupling constants o f a series of neutral radicals consisting of ten S,N-heterocyclic comp ounds were investigated by means of density functional theory (DFT), T he molecular geometries were optimized by gradient corrected DFT (UB3L YP) methods and isotropic hyperfine coupling constants (hfccs) were ca lculated through the Fermi contact analysis. The basis sets were 6-31G (d) and TZVP. The hfcc values were compared with experimental data and with theoretical results obtained by semi-empirical quantum chemical calculations (AM1/UHF and INDO/UHF) and by ab initio quantum chemical calculations (UMP2, UMP3 and UMP4). The results from DFT are highly su perior to those of the semi-empirical methods. As shown for 1,3,2-thia diazolyl, the computationally more demanding ab initio calculations do not provide better results with the same basis sets.