Embedded-cluster study of Cu+-induced lattice relaxation in alkali halides

We use an embedded-cluster approach to study the lattice relaxation induced by a substitutional Cu+ impurity in alkali halides. The crystalline lattice is modeled as a quantum-mechanical molecular cluster embedded in a classical lattice. The cluster is treated by using the unrestricted Hartree-Fock approximation and the embedding lattice is described by the shell model. The relaxations are obtained by comparing the equilibrium configurations of the pure and Cu+-doped clusters. We found that, when the Cu+ ion is introduced into the alkali halides, the lattice relaxes in accordance with the free-ion size difference between the Cu+ ion and the host cation. The correlation correction does not make a significant contribution to the lattice relaxation. © 1992 The American Physical Society