Embedded-cluster study of the lithium trapped-hole center in magnesium oxide

The lithium trapped-hole center in magnesium oxide is studied by using the simulation program package icecap (ionic crystal with electronic clusters, automatic program). The defective crystal is simulated as a molecular cluster embedded in a shell-model lattice. The molecular cluster, which contains the trapped-hole center, is treated quantum mechanically by using the unrestricted Hartree-Fock approximation. Correlation correction is also included in the calculations. Different types and sizes of defect cluster are used to determine the equilibrium configurations of the defective lattice. The role of the correlation correction is found to be significant. The results show very consistently that the Li⁺ ion and the O^- ion (the O^2- ion with the trapped hole) move toward each other and the axial O^2- ion moves away from the Li⁺ ion.