Dense simple plasmas as high-temperature liquid simple metals

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Abstract
In this paper, we study the thermodynamic properties of dense plasmas considered as high-temperature liquid metals. The problems that have to be solved are the following: (1) calculation of the ‘‘average’’ electron-density profile around an ion in the plasma, (2) determination of a self-consistent average ionization of the plasma, (3) calculation of the pair interaction between two ions, and (4) calculation of the total Helmholtz free energy. The first point is approximately solved in the Mermin-Kohn-Sham (MKS) density-functional theory of thermal ensembles, for a single ion in a spherical cavity in jellium. A prescription is then proposed for calculating the average ionization as a function of density and temperature using the electron densities from the MKS scheme. This prescription is shown to work well when the electron structure of the plasma is simple (i.e., when the overlap of bound states is not too large, and when there is no resonance in the free spectrum). The use of a superposition of single-ion densities for the total charge density of the plasma, together with a cluster expansion of the kinetic and exchange-plus-correlation energy, leads to the definition of the pair interaction that is readily calculable. Finally, the structural (ionic) part of the free energy is obtained from the hypernetted-chain theory of fluids.