Novel ReSe semiconductor designed by structure prediction and phase diagram calculation.

Non-stoichiometric transition metal chalcogenides often have unexpectedly good semiconducting properties. In this paper, we focus on the seeking of potential semiconducting material in the ReSe system. The global and unbiased crystal structure searches were systematically conducted on ReSe material, using the advanced crystal structure prediction algorithms combined with the density functional theory. Three novel structures of ReSe were discovered within different pressures regions. The phase diagram of ReSe material was then constructed at pressure up to 200 GPa and temperature up to 2500 K, based on the quasi-harmonic approximation. We found ReSe possesses the trigonal P 3 ¯ m 1 symmetric structure at ambient pressure. Under further compression, it transits to the orthorhombic Pmmn structure at 87 GPa and then to the cubic P m 3 ¯ m structure at 129 GPa. The three new structures are all mechanically and thermodynamically stable within corresponding pressures regions. The low-pressure P 3 ¯ m 1 -ReSe manifests good semiconducting properties with the band gap of 0.162 eV, while the two high-pressure allotropes have metallic characteristics. The mechanical properties analyses suggest that special attention should be paid on the brittleness of the P 3 ¯ m 1 -ReSe structure, when it is used at high-stress conditions. This study sheds considerable light on the new structures and properties of the non-stoichiometric transition metal chalcogenides ReSe for future synthesis and further investigation. [ABSTRACT FROM AUTHOR]