First-Principles Estimation of Low-Pressure Superconductivity in KC2H8 Ternary Hydride

Very recently, much research progress has been made on the pressure-induced superconducting state in ternary hydrides. Herein, an ab initio study of the KC2H8 ternary system is presented at a pressure in the range of 0-100 GPa. Its structural, electronic, dynamical, and superconducting properties are investigated, demonstrating that, at low pressure, KC2H8 is dynamically stable in a clathrate structure with space group Fm(3) over bar m and exhibits superconducting behavior with critical temperatures T-c in the range of 4-94 K. The important role played by C- and K-derived phonon modes at low frequencies and H-derived phonon modes at high frequencies is highlighted. Moreover, through the analysis of the hydrogen isotope effect, the conventional phonon-mediated pairing mechanism in this system is proved.