An embedded cluster analysis was made of the lattice distortions introduced by a Pb2+ substitutional impurity in these crystals. Active clusters were used which contained more than 100 atoms and which were embedded in a quantum representation of the crystalline environment. Charge compensation was achieved by introducing a cation vacancy into the host lattice. Both nearest-neighbor and next-nearest-neighbor vacancy positions were considered, as well as the case where a vacancy and an impurity were well-separated from one another. Only in the first 2 cases did the impurity adopt an off-center equilibrium position. The distortion trends as a function of the host lattice were identified. These trends were then used to predict the expected distortions in similar crystals. Thus, Pb2+-doped RbF and KBr were found to behave according to expectations.

Quantum Mechanical Study of the Lattice Distortions Induced by Aliovalent Pb2+ Impurities in Alkali Halides. A.Aguado: Physica Status Solidi B, 2002, 229[3], 1335-47