Crystal Structure and Electronic Properties of Rhenium Disulfide**

The crystal structure and electronic properties of rhenium disulfide in the triclinic crystal system are investigated using density functional theory and pseudopotential theory. The calculated primitive cell parameters and angles within a local density approximation are shown to be in good agreement with the experimental data. It is established that the observed direct-gap character of rhenium disulfide is related to interband transitions at point X . The electron energy spectrum is characterized by many valleys. The electronic structure is mainly formed by the 3p- and 5d-states of sulfur and rhenium ions, respectively. The role of 5d-states increases while that of 3p-states decreases during the transition from the valence band to the conductance band. The observed structure is due to the low symmetry of the primitive cell and the numerous nonequivalent positions of its constituent ions.