Self-Consistent Cluster-Lattice Simulation of Impurities in Ionic Crystals
When simulating defects in ionic crystals by a finite cluster model, one always has a problem of taking account of the influence of the lattice beyond the cluster. Some cluster models consider only the defect and the nearest-neighbor ions. Some calculations approximate the lattice potential by a certain number of point charges and effective core potentials. Several approximations to the lattice potential in the region of the cluster were compared to the exact Madelung potential in the recent work of Winter et al.1 That study emphasized the influence of the surrounding lattice ions on the energy level splitting and geometry of the nearest-neighbor cluster. It was found that the error in the calculated nearest-neighbor distance for the pure host is proportional to the error in the lattice potential. Unlike the finite cluster model, ICECAP (Ionic Crystal with Electronic Cluster; Automatic Program)2,3 incorporates the polarization and the distortion of the surrounding infinite lattice with the electronic structure of the cluster self-consistently. ICECAP has been used to study the impurity Cu+ and Ag+ ions in alkali halides. The ground state energy, excited state energies and crystal field splitting were calculated. The interatomic potentials for impurities Cu+ and Ag+ in alkali fluorides and alkali chlorides were determined and used to study the transport properties.4,5
KeywordsLattice Potential Defect Cluster Effective Core Potential Correlation Correction Crystal Field Splitting
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