Prediction of pressure-induced superconductivity in the ternary systems YScH_2n(n=3-6)

Hydrogen-rich ternary compounds are promising candidates for realizing room-temperature superconductivity due to the synergistic effects of crystal structure and electronic properties under high-pressure conditions. Here, the high-pressure structures, electronic properties, and superconductivity of the ternary YScH2n (n = 3-6) system are investigated by using the prediction method of particle swarm optimization structure combined with first-principles calculations. We find four stable structures, each with different hydrogen sublattices: Pm3 over bar -YScH6, P4/mmm-YScH8, Cmmm-YScH10, and Pm to be high-temperature superconductors. The electron local function (ELF) results indicate a lack of interaction between hydrogen atoms in YScH6, while the weak H -H covalent interactions are observed in the other stoichiometric ratios. Strikingly, YScH6 maintains dynamic stability down to ambient pressure and keeps a high superconducting critical temperature (Tc) of 66 K. At 140 GPa, the pressure-stabilized YScH8 and YScH10 structures exhibit high Tc of 110 and 116 K, respectively. Upon further increasing the content of hydrogen, the lowest dynamically stable pressure of YScH12 is increased to 200 GPa, and the calculated Tc is up to 179 K. In all YScH2n structures, Pm3 over bar -YScH6 (stabled from 1 atm to 47 GPa), P4/mmm-YScH8 and Cmmm-YScH10 (stabled from 140 to 250 GPa), Pm3 over bar m-YScH12 (stabled from 200 to 286 GPa), strong electron-phonon coupling (EPC) and large electronic density of states of hydrogen at the Fermi level play important roles in their high-temperature superconductivity. It is discussed that phonon softening in the midfrequency region induced mainly by Fermi surface nesting effectively enhances the EPC. In this paper, we potentially discover high-temperature superconducting hydrides that can be stable at atmospheric pressure, taking an important step toward understanding the superconductivity and structural stability of ternary hydrides. 3 over bar m-YScH12. All these YScH2n structures are predicted