Phase Diagram and Electrical Conductivity of High Energy-Density Water from Density Functional Theory

The electrical conductivity and structure of water between 2000–70 000  K and 0.1–3.7  g/cm³ is studied by finite temperature density functional theory (DFT). Proton conduction is investigated quantitatively by analyzing diffusion, the pair-correlation function, and Wannier center locations, while the electronic conduction is calculated in the Kubo-Greenwood formalism. The conductivity formulation is valid across three phase transitions (molecular liquid, ionic liquid, superionic, electronic liquid). Above 100 GPa the superionic phase directly borders an electronically conducting fluid, not an insulating ionic fluid, as previously concluded. For simulations of high energy-density systems to be quantitative, we conclude that finite temperature DFT should be employed.