In-silico synthesis of lowest-pressure high-Tc ternary superhydrides

We report the theoretical prediction of two high-performing hydride superconductors BaSiH8 and SrSiH8. They are thermodynamically stable above pressures of 130 and 174 GPa, respectively, and metastable below that. Employing anharmonic phonon calculations, we determine the minimum pressures of dynamical stability to be around 3 GPa for BaSiH8 and 27 GPa for SrSiH8, and using the fully anisotropic Migdal-Eliashberg theory, we predict Tc’s around 71 and 126 K, respectively. We also introduce a method to estimate the lowest pressure of synthesis, based on the calculation of the enthalpy barriers protecting the BaSiH8 3¯ structure from decomposition at various pressures. This kinetic pressure threshold is sensibly higher than the one based on dynamic stability, but gives a much more rigorous limit for synthesizability.