Nuclear Quantum Effects in Two-temperature Hydrogen via Orbital-free DFT Path Integral MD

Among systems at extreme conditions, hydrogen is special: its small nuclear mass implicates significant nuclear quantum effects (NQEs). An increasingly important set of extreme-condition systems has electrons driven to temperature T_e far from the ion temperature T_i. For such two-temperature hydrogen, we report path integral molecular dynamics calculations driven by state-of-the-art orbital-free DFT calculations for the electrons. When the ratio of the ionic thermal de Broglie wavelength to their mean distance is larger than about 0.35, the ionic radial distribution function is strongly affected by NQEs. Moreover, NQEs induce a substantial increase in both the ionic and electronic pressures.