g-tensor and hyperfine splitting of { Cl}₂⁻ , { O}₂⁻ , { N}₂⁻ defect centers in KCl from DFT calculations

We have studied the electron paramagnetic resonance (EPR) properties of a classical group of paramagnetic centers in solid KCl, the H center (a trapped Cl(2)(-) species) and the analogous O(2)(-) and N(2)(-) centers. The calculations have been performed at the density functional theory level using pure and hybrid exchange-correlation functionals in combination with cluster models embedded in point charges. The attention has been focused on the reproduction of key EPR parameters such as the g-and the A-tensors. The A-tensor is satisfactorily reproduced for all three species. The g-tensor is well described in the case of the H center, while large deviations are found for the O(2)(-) and N(2)(-) trapped radicals. The different behavior is rationalized in terms of different symmetries of the singly occupied molecular orbitals, s in Cl(2)(-) and p in O(2)(-) and N(2)(-).