Nearest-neighbor approximation in the thermodynamics of coulomb systems and plasmas

A method is proposed for calculating the thermodynamic characteristics of many-particle systems with explicit separation of the nearest-neighbor interaction. This method is used to obtain a group expansion for the distribution function of the micropotential, the logarithm of the probability density of the nearest neighbor, and the characteristic function (the Fourier transform of the distribution function of the micropotential) and this describes the influence of the remaining particles. For a Coulomb system, the explicit form of these quantities in the ring approximation is found. The density of electron states calculated in this manner is finite at all energies and describes a transition from bound to free states.