Superconductivity of hydrogen superoxide under high pressure

We explored the superconductivity in a oxygen-hydrogen binary system, H_hO_1 − h, under highpressure using an evolutionary algorithm-based materials informatics approach. We searched for metallic and superconducting phases in pressures up to 300 GPa using a crystal structure prediction technique based on a genetic algorithm and first-principles calculations, and found that hydrogen superoxide (HO₂) with an orthorhombic Pnnm, which emerges as a metastable compound in pressure above 180 GPa, is the only compound showing the superconductivity. The superconducting critical temperature $T_c$ is 9.78 K at 200 GPa, which is higher than that of pure solid oxygen, 2.87 K, due to the effect of the hydrogenation. We confirmed that the $T_c$ value shows a good agreement with potential superconducting critical temperature $T_c^{pot}$ estimated by the superconductivity predictor, which we have previously developed by a genetic programming using 497 first-principles datasets of other binary hydrides. Moreover, supposing that all the H_hO_1 − h compounds are superconductors at pressures in 150–200 GPa, we investigated the potential superconductivity of the H_hO_1 − h system using the predictor and obtained that $T_c^{pot}$ shows 10 K for h = 0.033 3 and increases to 100 K with the increase of h to 0.966 7. (paper)