QUANTUM CHEMICAL SIMULATION OF THE SELF-TRAPPED HOLE IN ALPHA-AL2O3 CRYSTALS

Atomistic simulations of hole self-trapping in a pure corundum crystal have been undertaken using three different approaches. The inward Jahn-Teller displacement of two O atoms (on which 80% of the hole density is concentrated), accompanied by the outward displacement of the two nearest Al atoms, gives the energetically most favorable configuration, thus suggesting a self-trapped-hole (STH) model analogous to that in alkali halides (V(K) center). The optical absorption of STH and three possible kinds of thermally activated hops are discussed in relation to experimental data.