Dynamical and optical properties of warm dense hydrogen

We report dynamical and optical properties of hydrogen (deuterium) around the region of the principal Hugoniot that starts from the cryogenically cooled molecular liquid. These properties were determined by finite-temperature density functional (FTDF) molecular dynamics (MD) simulations within the local density and generalized gradient approximations. The principal Hugoniot, calculated from the FTDF-MD equation of state, agrees with gas-gun and recent laser-shock experiments for pressures up to 50 GPa. However, the maximum compression of the FTDF-MD Hugoniot (4.6 at 52 GPa) significantly differs from that of the laser shock experiment (6 at about 150 GPa). On the other hand, the optical reflectivities show reasonable agreement with the laser measurements for pressures up to 70 GPa. The system smoothly dissociates along the Hugoniot with the electrical conductivity reaching a value of 4000 Ω^-1 cm^-1 at maximum compression. We also obtain good agreement with previous tight-binding and ab initio molecular dynamics studies.