Equation of state, ionic structure, and phase diagram of warm dense krypton.

Extensive quantum molecular dynamics (QMD) simulations are performed to determine the equation of state, sound velocity, and phase diagram of middle-Z krypton in a warm dense regime where the pressure (rho) is up to 300 GPa and the temperature is up to 60 kK. The shock wave experimental data are used to validate the present theoretical models. It is found that, within the regime of the current density (rho) and temperature (T), sound velocity can effectively discriminate differences between different theoretical models, and therefore it is more suitable as a benchmark to verify the practicability of models. The QMD-simulated results of the ionic structures and electronic properties imply the occurrence of two kinds of phase transitions, including transition from a solidlike to fluid state and that from an insulator to conductive fluid in this T-P regime. The calculated electrical conductivities confirm that the metallization transition occurs at about 60 GPa and 17.5 kK along the principal Hugoniot. With the help of simulation results and experimental data, a comprehensive phase diagram for krypton is constructed by using the solid-fluid and insulator-metal fluid phase boundaries, which fills the gap of the experimental work [Proc. Natl. Acad. Sci. USA 112, 7925 (2015)]. These results will provide an instructive basis for the experimental investigations of rare gases over a wide T-P range.