Various models are used in order to develop an accurate equation of state (EOS) for stellar matter (see e.g. Saumon and Chabrier 1991). The complexity of physical effects, for instance degeneracy, relativity, Coulomb- and non-Coulombic interactions requires detailed knowledge from the many-particle physics.
For many applications it is desirable to have theories for these effects over a wide range of densities and temperatures. One of the main sources of uncertainties in the EOS models is the exchange-correlation contribution at any degeneracy and relativity. Previous investigations determine thermodynamic quantities of a partially (e.g. Graboske et al. 1969, Kraeft et al. 1986, Däppen et al. 1988) or fully ionized (e.g. Hubbard and DeWitt 1985, Ichimaru et al. 1987) plasma, resp. Interpolation procedures (Magni and Mazzitelli 1979, Fontaine et al. 1977) combine both cases in the EOS but show non-continuous behaviour.