Knowledge Bank

A simple analytic method is developed for calculating the electronic contribution to the energy and pressure of elements and mixtures of elements. Two atomic models and statistics are used in the method: (1) a hydrogenic model with continuous energy levels using Maxwell-Boltzmann statistics and (2) a zero-temperature Thomas-Fermi model using Fermi-Dirac statistics. The equations of state computed from the two models are combined in a simple manner which is dependent on the free electron degeneracy parameter. The results agree within a few percent with $R.Latter\prime s1$ exact numerical solution, expept at low temperatures and high densities due to the neglect, in this paper, of the influence of the free electrons on the ionization potential. This is, however, not of much practical importance since the electronic contribution to the equation of state is insignificant in that region.