Basic Chemical Models of Nonideal Atomic Plasma
  The concept of basic chemical models is introduced, which is new from the standpoint of the physics of nonideal atomic plasma. This concept is based on the requirement of full conformity of the expression for free energy in the chemical model of plasma to exact asymptotic expansions obtained in the grand canonical ensemble within the physical model of plasma. The thermodynamic functions and equations of state and ionization equilibrium are obtained for three basic chemical models differing from one another by the choice of the atomic partition function. Comparison is made with the experimental results for nonideal plasma of cesium and inert gases. It is demonstrated that the best fit to experiment is shown by the results obtained using a basic chemical model with atomic partition function in the nearest neighbor approximation with classical determination of the size of excited atom. 
A. L. Khomkin, I. A. Mulenko, and A. S. Shumikhin