Electron–ion pairs in thermodynamics of nonideal Coulomb systems and plasmas

A model including formation of electron–ion pairs with positive and negative internal energies in a classical system of Coulomb particles and a plasma is suggested. Within the suggested approach we calculate the thermodynamic functions of the model Coulomb system for which numerical data are available, obtained by the Monte-Carlo method. The deviations from Debye's theory obtained in the numerical calculations are explained by the formation of electron–ion pairs. A four-component model of an atomic nonideal plasma is suggested. Electron–ion pairs are added to the traditionally considered electrons, ions, and atoms. The pressure and composition of a hydrogen plasma are calculated under conditions of substantial Coulomb nonideality, and comparison to the calculated results in a large canonical ensemble shows them to be very close to the experimental values. The presence of a saturation effect of Coulomb nonideality is demonstrated.