Klockmannite, CuSe: structure, properties and phase stability from ab initio modeling.

The details of the electronic and crystal structure, the nature of the interatomic bonding and the phase stability of three modifications of klockmannite, CuSe, are analysed using first principles modeling. The hexagonal modification of CuSe is predicted to be less stable than the orthorhombic phase under pressure. The stabilizing force for the orthorhombic phase is identified as the Cu-Cu bond formation between the Cu atoms in the flat hexagonal CuSe layer and in the buckled Cu(2)Se(2) layer. Furthermore, klockmannite is shown to be unstable under compression with respect to the decomposition into umangite, Cu(3)Se(2), and krutaite, CuSe(2) II.