Theoretical and experimental refraction index of shock compressed and pre-compressed water in the megabar pressure range

Abstract

The refraction index of water at megabar pressures was calculated ab initio with the quantum molecular dynamics (QMD) package ABINIT using the projector augmented (PAW) formalism. Calculations were compared to experimental results obtained by laser-driven shocks on water in standard conditions and on water samples statically precompressed at ${\approx}10\ \text{kBar}$ . The refraction index was measured in transparent and opaque states of water using a VISAR diagnostics. We also modelled the data using an extended Lorentz-Drude model. At high compressions, a strong increase of the refraction index is observed both in experimental results and in the theoretical calculations, which is an indication of water approaching band gap closure