Electronic structure of rhombohedral

The band properties of corundum-phase have been calculated in the local-density approximation with the use of the linear augmented-plane-wave method. The results consist of low-lying O 2p states and a partially filled complex near where metallic behaviour originates from overlapping and subbands. Decreasing the c/a ratio (even beyond the observed low-temperature value) reduces but does not eliminate this - band overlap, thereby precluding a band explanation for the metal - insulator transition that is observed in this system with no accompanying structural distortion.