Metalization of Warm Dense Polystyrene Along the Principal Hugoniot

Using recently developed thermal meta-GGA exchange-correlation (XC) density functional, T-SCAN-L, we perform fully consistent density functional theory simulations to investigate equation of state up to 7 Mbar and the insulator-metal transition (IMT) of shocked polystyrene (CH) along the principal Hugoniot. CH is often used as an ablator material in inertial confinement fusion (ICF) experiments; therefore, its properties in warm dense conditions are crucial for ICF target designs. Our results are compared with an OMEGA experiment as well as the results obtained from the zero-temperature PBE XC. We show that the inclusion of thermal and inhomogeneity effects at the meta-GGA level via T-SCAN-L XC significantly improves the agreement with the IMT dynamics in terms of the behavior of optical reflectivity observed in the OMEGA experiment. Analysis of the pair correlation functions suggests that the IMT is driven by the molecular dissociation of CH that occurs in the pressure range of 1 to 2 Mbar and apparently coincides with the turn-on of optical reflectivity and dc conductivity that is accompanied by the respective band-gap closure.