  Recent discovery of high-temperature superconductivity (Tc = 190 K) in sulfur
hydrides at megabar pressures breaks the traditional belief on the Tc limit of
40 K for conventional superconductors, and open up the doors in searching new
high-temperature superconductors in compounds made up of light elements.
Selenium is a sister and isoelectronic element of sulfur, with a larger atomic
core and a weaker electronegativity. Whether selenium hydrides share similar
high-temperature superconductivity remains elusive, but it is a subject of
considerable interest. First-principles swarm structure predictions are
performed in an effort to seek for energetically stable and metallic selenium
hydrides at high pressures. We find the phase diagram of selenium hydrides is
rather different from its sulfur analogy, which is indicates by the emergence
of new phases and the change of relative stabilities. Three stable and metallic
species with stoichiometries of HSe2, HSe and H3Se are identified above ~120
GPa and they all exhibit superconductive behaviors, of which the hydrogen-rich
HSe and H3Se phases show high Tc in the range of 40-110 K. Our simulations
established the high-temperature superconductive nature of selenium hydrides
and provided useful route for experimental verification.
