Phase behaviours of superionic water at planetary conditions

Most water in the Universe may be superionic, and its thermodynamic transport properties are crucial for planetary science but difficult to probe experimentally or theoretically. We use machine learning free-energy methods overcome limitations of quantum mechanical simulations characterize hydrogen diffusion, superionic transitions phase behaviours at extreme conditions. predict that close-packed phases, which have a fraction mixed stacking finite systems, stable over wide temperature pressure range, whereas body-centred cubic is only thermodynamically small window kinetically favoured. Our boundaries, consistent with existing—albeit scarce—experimental observations, help resolve fractions insulating ice, different phases liquid inside ice giants. Superionic believed exist interior giant planets. By combining methods, pressures temperatures prevalent such planets predicted.