Perturbation theory of a classical one-component plasma
We have extended a recent perturbation theory (J. Chem. Phys. 82, 414 (1985); 84, 4547 (1986)) for nonionic systems to the one-component plasma (OCP). Characteristic features of the theory are its ability to handle both fluids and solids and the use of a reference potential whose repulsive range shrinks with density. Based on the computed thermodynamic data, we have developed a simple alternative (optimized hard-sphere) model, whose Helmholtz free energy is a sum of the Helmholtz free energy of the hard-sphere reference system and the Madelung energy of a fcc lattice. Comparison with available Monte Carlo and other theoretical results shows that the optimized hard-sphere model gives reliable solid (fcc) and fluid properties. The theory predicts that the fcc solid will melt at the Coulomb coupling parameter GAMMAsub m/ = 208 versus Helfer et al.'s (J. Stat. Phys. 37, 577 (1984)) Monte Carlo value of 196. This difference is due to a small difference (0.1%) in the computed excess free energy. The computed internal energy can be accurately fitted by an analytic form. Its two leading terms (for the fluid) are -0.899488GAMMA1.272 97GAMMAsup 1/4/, in close agreement with Slattery et al.'s (Phys. Rev. A 21, 2087 (1980); 26, 2255 (1982)) empirical fit to their Monte Carlo data. We conclude that the hard-sphere perturbation theory is applicable to a long-range repulsive system, such as the OCP, so long as the hard-sphere diameter is judiciously chosen by using a density-dependent reference potential.
- Research Organization:
- Lawrence Livermore National Laboratory, University of California, Livermore, California 94550
- OSTI ID:
- 6642211
- Journal Information:
- Phys. Rev. A; (United States), Vol. 38:11
- Country of Publication:
- United States
- Language:
- English
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