Superconductivity of hydrogen superoxide under high pressure

We explored the superconductivity in a oxygen-hydrogen binary system, HhO1 - 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 HhO1-h compounds are superconductors at pressures in 150-200 GPa, we investigated the potential superconductivity of the HhO1-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.