A TECHNIQUE FOR EMBEDDING CLUSTERS IN IONIC CRYSTALS USING THE GAUSSIAN 92 QUANTUM CHEMICAL PROGRAM

摘要

We present a technique for embedding clusters of atoms, which are to be treated quantum mechanically, in ionic crystals by representing the external lattice by classical lattice-centered Gaussian charge distributions. The goal is to carry out ab initio self-consistent field calculations of the many-electron ground and excited states of finite clusters representing defects in an otherwise perfect crystal lattice. We describe a procedure for determining the effective charges and Gaussian exponents describing the external lattice so that, together with Hartree-Fock force calculations, the net forces on the quantum mechanical cluster ions are zero in the ground stale. The result of this procedure is the production of an external coulombic field that has the same symmetry as the crystal, exactly balances the quantum mechanical forces, and simultaneously accounts for the fact that the external charge distribution is finite. The method is illustrated by considering the formation of the F-center defect in CaF2. (C) 1996 Academic Press, Inc. [References: 18]