First-principles study on structural, mechanical and electronic properties of thorium dichalcogenides under high pressure

Abstract By merging a b i n i t i o calculations and particle-swarm optimization algorithm, we have predicted two new phases of thorium dichalcogenides ThX 2 (X = S, Se and Te) in the F m 3 ¯ m and I 4 / m m m symmetry. The F m 3 ¯ m phase is proved to be the ground-state phase of ThS 2 and ThSe 2 . The calculated enthalpies indicate that the F m 3 ¯ m to P n m a phase transition pressures are about 2.3 GPa and 0.35 GPa for ThS 2 and ThSe 2 , respectively; and the P n m a to I 4 / m m m phase transition pressures are about 37 GPa, 17 GPa and 2 GPa for ThS 2 , ThSe 2 and ThTe 2 , respectively. The phonon dispersion curves and elastic constants suggest that all of the F m 3 ¯ m , P n m a and I 4 / m m m phases are dynamically and mechanically stable. The electronic calculations show that a pressure-induced semiconductor to metal transitions of these three compounds will occur following the P n m a to I 4 / m m m phase transition. Our calculated bulk modulus B 0 and elastic constants C i j of the various phases of these compounds show that the materials become softer one after another from ThS 2 to ThSe 2 and then to ThTe 2 .