The importance of excited states in the thermodynamics of partially ionized plasma

The expansion of thermodynamic functions into series in terms of degrees of activity in the grand canonical ensemble is used to consistently include the contribution of highly excited states to partial thermodynamic functions of atomic plasma components and to the equation of ionization equilibrium. It is demonstrated that, when the nearest neighbor approximation is used to calculate the atomic partition function, the corrections due to the interaction of charges in continuous spectrum vary considerably compared with the traditionally employed models. No Debye asymptotics are observed either in the decrease of the ionization potential or in the corrections to the charged component pressure.