Theoretical investigation of the structure of κ-${\mathrm{Al}}_2$${\mathrm{O}}_3$

Using plane-wave pseudopotential calculations based on density-functional theory at the local-density-approximation level we investigate all the possible κ-${\mathrm{Al}}_2$${\mathrm{O}}_3$ structures which are permitted by the known crystal symmetry. We find that structures with sixfold coordinated Al atoms are significantly more stable than those having any or all of the Al atoms in fourfold coordinated sites. This is in agreement with preliminary experimental results.