Dependence of the radical g-tensor on the molecular environment. Sulfur-centered radicals of thiocytosine in the cytosine crystal matrices

The g-tensor parameters for thiocytosine radical in crystal matrices have been calculated with the use of the B3LYP/6-311G(2d,p) density-functional (DFT) method and basis set both for geometry optimizations and single point calculations. The theoretically derived g-tensor principal values as well as direction cosines fit well to the experimental data, if in the calculations the spread of the spin density over the molecules neighboring the “radical” is taken into account. Much better agreement with the experiments is achieved when more molecules are included in the calculation. Special care has to be taken in truncation of the lattice surrounding the “radical”, the procedure needed to reduce the system to the size suitable for the calculation. Generally, better results could be achieved for partially optimized structures, allowing for possible restructuring near the radical site.