Revisiting metallization boundary of warm dense helium in a wide ρ-T regime from ab initio study

The knowledge of the metallization of warm dense helium has important implications for understanding the thermal histories, stellar structure and magnetic field environment of giant planets. However, it is also a pendent scientific topic. For a revisiting into the properties of warm dense helium, we performed extensive quantum Langevin molecular dynamic simulations and electronic structure calculations to study helium over a very wide range of density (ρ = 1~24 g/cm³) and temperature (T = 10~160 kK). The dependencies of helium band gap on ρ and T were presented and a metallization boundary of helium was thus determined by gap closure. Such a boundary is further identified by the calculated electrical conductivity and optical reflectivity based on Kubo-Greenwood formula: along the boundary, the electrical conductivities are found to be 7.0 × 10⁵~1.3 × 10⁶ Ω^-1 m^-1 and the optical reflectivity value at 532 nm is about 0.55, which are typical values for true metal.