The equation of state and composition of matter are calculated for conditions typical for pre-collapse and early collapse stages in core collapse supernovae. The composition is evaluated under the assumption of nuclear statistical equilibrium, when the matter is considered as an `almost ideal gas with corrections due to thermal excitations of nuclei, to free nucleon degeneracy, and to Coulomb and surface energy corrections. The account of these corrections allows us to obtain the composition for densities a bit below the nuclear matter density. Through comparisons with the equation of state (EOS) developed by Shen et al. we examine the approximation of one representative nucleus used in most of recent supernova EOSs. We find that widely distributed compositions in the nuclear chart are different, depending on the mass formula, while the thermodynamical quantities are quite close to those in the Shens EOS.
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