Thermodynamics and Phase Transitions in Dense Hydrogen - the Role of Bound State Energy Shifts

In recent papers we have investigated the effects of Pauli blocking on the energy shifts in dense hydrogen. As Pauli blocking we denote effects on the shifts which result from the antisymmetry of the electronic wave functions. Here we study of the thermodynamic properties of dense hydrogen including the influence of energy shifts. Of special interest is the region where a transition from insulating behavior to metal-like conductivity has been shown experimentally. In this region, Pauli blocking effects have a deciding influence on this transition. Assuming that the system is a gas-like mixture of chemical species, the ionization equilibrium is treated by an advanced chemical approach. We calculate the Pauli and Fock shifts by perturbation theory and variational methods and construct useful interpolation formulae. Results for the ionization equilibrium are presented for temperatures between 4 000 K < T < 20000 K and densities in the range n = (2 - 6) x 10(23)cm(-3) where the transition from a neutral hydrogen gas to a highly ionized plasma occurs. The results for the equation of state and the relative pressure indicate that the transition to a highly conducting state is softer than derived in earlier work. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim