Ab initio study of deuterium in the dissociating regime: sound speed and transport properties.

Abstract

The sound speed and the transport properties of dense hydrogen (deuterium) are computed from local spin-density approximation molecular-dynamics simulations in the dissociating regime. The sound speed c(s) is evaluated from the thermodynamical differentiation of the equation of state in the molecular phase and is in very good agreement with recent experiments. The diffusion constant D and the viscosity eta are extracted from simulations performed at V=6, 4, and 2.7 cm(3)/mole, corresponding, respectively, for deuterium at rho=0.672, 1.0, and 1.5 g/cm(3) in a range of temperatures 1000 K<T<50,000 K. In the dissociated regime, the diffusion coefficient is well predicted by one-component plasma formulas using a renormalized coupling parameter recently proposed by Murillo [M. S. Murillo, Phys. Rev. B 62, 4115 (2000)]. The behavior of the shear viscosity in the dissociated regime is more complex and exhibits a crossover between atomic and screened plasma formulation. A comparison with recent molecular-dynamics simulations of Yukawas systems shows that the inverse of the screening length must lie between 1 and 2, in nearest-neighbor radius units, as suggested by the results on the diffusion.