The equation of state ( EOS ) for partially ionized carbon , oxygen , and carbon-oxygen mixtures at temperatures 3 \times 10 ^ { 5 } \mbox { ~ { } K } \lesssim T \lesssim 3 \times 10 ^ { 6 } K is calculated over a wide range of densities , using the method of free energy minimization in the framework of the chemical picture of plasmas .
The free energy model is an improved extension of our model previously developed for pure carbon ( Phys .
Rev .
E 72 , 046402 ) .
The internal partition functions of bound species are calculated by a self-consistent treatment of each ionization stage in the plasma environment taking into account pressure ionization .
The long-range Coulomb interactions between ions and screening of the ions by free electrons are included using our previously published analytical model , recently improved , in particular for the case of mixtures .
We also propose a simple but accurate method of calculation of the EOS of partially ionized binary mixtures based on detailed ionization balance calculations for pure substances .