Calculation of hyperfine coupling constant and the g tensor of alanine radicals at different crystal temperatures based on Density Functional Theory (DFT)

In this paper, Density Functional Theory (DFT) was utilized for the calculation of the hyperfine coupling constant and the g tensor alanine radicals at different crystal temperatures. The cluster approach was used for considering the effects of crystal environment. In the cluster approach, the careful selection of the cluster size is very important for the geometry structure of alanine and the EPR parameters of alanine radicals. The geometry structure of alanine and the EPR parameters of alanine radicals showed a good agreement with the experiment data when 6 alanine molecules had hydrogen bonds with the central alanine or alanine radicals. Further, bigger clusters could even lead to an incorrect description of the geometry structure of alanine and EPR parameters of alanine radicals in the condensed phase.