First-principles study of osmium under high pressure

Considering the effect of spin - orbit coupling, we have studied the equation of state, structural parameters and electronic structures of osmium under high pressure by first-principles plane-wave basis pseudopotential calculations. We find the following: (1) the calculated bulk modulus is less than that of diamond, and the value becomes smaller after taking into account the spin - orbit coupling; (2) the proposed isostructural phase transition (c/a ratio anomaly) around 25 GPa is not supported by the present calculations. By analysing the band structure, the density of states at the Fermi surface, and the equation of state for the cases with and without spin - orbit coupling, we find no electronic topological transition up to 150 GPa.