Semiempirical Calculations of the Impurity Level Positions with Respect to the Perfect Crystal Bands

The semiempirical calculation of the electronic structure of a perfect KCl crystal carried out within the framework of the large unit cell model is compared with those performed using the cluster model. The positions of the ground state one‐electron levels of the impurity ions Tl⁺ and Tl²⁺ within the gap are also calculated using molecular clusters of different sizes. The procedure which takes into account the crystal lattice polarization produced by a charged impurity is proposed for the calculation of Tl²⁺ levels. The electronic density distributions and the impurity level positions with respect to the KCl bands are compared for both the defects.